Introduction, general terms,reproduction, gametogenesis, HELENA NEJEZCHLEBOVÁ, helanej@sci.muni.cz BI6140EN EMBRYOLOGY This material is intended only for students of Bi6140en Embryology (spring 2025). Free distribution prohibited. THANK YOU. Embryology § study of the individual development (ontogenesis) of the embryo from an fertilized egg; § study of the formation and development of an embryo and fetus to the hatching/birth of a new individual; § study of the development of a fertilized egg into the complex of interdependent system of organs that contribute to adult animal §„embryon“ (gr.); embryo = formation developing from a fertilized egg cell, a formation formed by the first mitosis of the zygote; § „foetus“ (lat.); fetus = unborn vertebrate (mammal), the fetal period follows the embryonic § embryology: descriptive, comparative, experimental (microsurgical experiments), … § Importance of embryology: a) broadening and deepening our knowledge b) knowledge of factors, mechanisms and critical periods in ontogenesis is of great importance for the healthy development of individuals (prevention of congenital malformations, infertility treatment,…) c) clarifies how normal and abnormal structures develop d) knowledge of prenatal development is necessary for a number of professions: vets, scientists, embryologists, obstetricians, pediatricians, surgeons,… 2 BI6140EN EMBRYOLOGY Hall of Fame ◦Aristotle (384-22 B. C.): §founder of biology as a science §1st textbook of reproductive biology De generatione animalium (On animal reproduction) §1st written records of the developing organisms: incubated and observed chicken eggs at various stages of development, he described the gradual formation of a shape from an unstructured mass §his theory of the origin and development of animals is very complex, it includes plants and animals, but also spontaneous births - generatio spontanea (lat.): life arising from non-living matter, mice born of mud or butterflies of dewdrops etc. ◦ ◦Claudius Galenus(130-200 A. D.): §theory of male and female semen https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Aristotle_Altemps_Inv8575.jpg/220px-Arist otle_Altemps_Inv8575.jpg https://cs.wikipedia.org/wiki/Aristotel%C3%A9s BI6140EN EMBRYOLOGY ◦William Harvey (1578-1657): § 1st person who recognized the full circulation of the blood in humans, rejected the theory of spontaneous birth formulated by Aristotle § "Omne vivum ex ovo" (all animals develop from an egg, but was unable to prove its existence) §De Generatione Animalium (1651): the beginning of the "embryological revolution", WH believed that sperm after entering the uterus metamorphose to form an embryo ◦Antony van Leeuwenhoek (1632-1723): §amateur researcher, founder of microscopic anatomy, „father of mikrobiology“, discovered sperm, follower of preformism (= ontogenesis is the unpacking of preformed forms): supposed to observe all parts of man in the embryo and sperm (homunculi), similarly leaves / flowers are present in seeds ◦Marcello Malpighi (1628-1694): §observed homunculi in eggs J, thought that unfertilized chicken eggs contained miniature chickens ◦ Lazarro Spallanzani (1729-1799): §1st artificial fertilization (frog) and insemination (dog), proven importance of egg and sperm, refused theory of preformisn and spontaneour birth ◦ Carl Linné (1707-1778): §plant pollination experiments (1740) § http://freethoughtblogs.com/pharyngula/files/2015/02/leeuwenhoek.jpg http://freethoughtblogs.com/pharyngula/files/2015/02/leeuwenhoek.jpg, https://cs.wikipedia.org/wiki/William_Harvey Hall of Fame BI6140EN EMBRYOLOGY ◦Carl Ernst von Baer (1791 – 1876): §microscopic description of a mammalian egg (1827) § comparison of embryonic development in mammals → Baer's ontogenetic law: general features common to large groups occur earlier in embryos than specialized features; embryos of different species differ more and more during development ; early embryo of „a higher animal“ (phylotypic stage) is similar to the early embryo of „a lower animal“, not an adult ◦J. E. Purkyně (1787–1869): §egg nucleus description („vescicola germinale“) ontogeny Hall of Fame http://www.rustreg.upol.cz/_materials/vbi/10_Vyskot_Evodevo.pdf BI6140EN EMBRYOLOGY Hall of Fame ◦Rudolf Virchow (1821-1902): cell theory: „Omnis cellula ex cellula“ ◦Ernst Haeckel (1834-1919): biogenetic law (recapitulation theory): ontogeny recapitulates phylogeny ◦August Weismann (1834-1914): germ plasma continuity theory, ie. germ cell lines = immortal "germen", transmitted through the mortal body ◦Oscar and Richard Hertwig (19./20. stol.): study of fertilization (model organism: sea urchin, zygote comes from the union of two different germ cells), mesoblast: middle germ leaf ◦O. Hertwig (1875): fertilization ← a single sperm, 1890 description of the stages of meiosis cell theory http://ezlinking.blogspot.cz/2013/04/cell-theory_22.html BI6140EN EMBRYOLOGY v roce 1876: oplodnění zahrnuje pronikání spermie do vaječné buňky. Hall of Fame ◦Theodor Boveri (1862-1915): chromosome theory: defined nuclear complexes with different effects on different cells ◦Thomas Hunt Morgan (1866 - 1945): model Drosophila, 1933: Nobel Prize as the first biologist! ◦Hans Spemann (1869-1941): amphibian research, embryonic induction (1924) = the ability of a embryonic tissue to induce differentiation of another tissue, 1935: Nobel Prize ◦Sydney Brenner (1927): model organism Caenorhabditis elegans, 2002: Nobel Prize; interesting videos about the importance of Caenorhabditis elegans in biology: http://www.jove.com/science-education/5110/c-elegans-development-and-reproduction and http://www.jove.com/video/2852/time-lapse-microscopy-of-early-embryogenesis-in-caenorhabditis-elega ns ◦Robert Edwards and Patrick Steptoe (1978): Louise Brown (UK) is the first "test tube baby" in the world; R. Edwards (2010): Nobel Prize in Physiology and Medicine, (Steptoe died 1988); Luisa's birth raises a number of questions → 1984 Warnock Report (model document for assisted reproduction legislation in the UK and other countries) BI6140EN EMBRYOLOGY http://www.jove.com/science-education/5110/c-elegans-development-and-reproduction http://www.jove.com/video/2852/time-lapse-microscopy-of-early-embryogenesis-in-caenorhabditis-elega ns Model organisms in embryology § Model organisms: their research serves to acquire information about these species, but also to study general phenomena and derive laws applicable to other organisms. The study of these species has enabled significant discoveries in many disciplines, including embryology and developmental biology, with far-reaching implications for practice § Important model species include: § worm (Caenorhabditis elegans, Phylum: Nematode) § fruit fly (Drosophila (“dew lover”) melanogaster (“dark gut”), Phylum: Arthropod) § sea urchin (genus Echinus, Phylum: Echinoderm) § zebrafish (Brachydanio rerio, Phylum: Chordate) § African clawed frog (Xenopus laevis, Phylum: Chordate) § chicken (Gallus gallus domesticus, Phylum: Chordate) § mouse (Mus musculus, Phylum: Chordate) § Rattus norvegicus (Phylum: Chordate) § dog (Canis lupus familiaris, Phylum: Chordate) § 8 BI6140EN EMBRYOLOGY alternativní popis obrázku chybí https://cs.wikipedia.org/wiki/Dr%C3%A1patka_vodn%C3%AD, https://cs.wikipedia.org/wiki/D%C3%A1nio_pruhovan%C3%A9, https://en.wikipedia.org/wiki/Laboratory_rat alternativní popis obrázku chybí https://upload.wikimedia.org/wikipedia/commons/1/1d/Albino_Rat.jpg Model organisms in embryology § Why we generally do not study prenatal development in humans?: observation of embryos/fetuses is difficult inside body; morally and ethically problematic; experimental procedures very limited in humans § → model organisms: similarities in the development of very different organisms; the eggs of different model organisms vary in size and design, but the overall design and body plan is very similar among embryos; model organisms allow understand a broad spectrum of biological principles or answer particular questions; § advantages: easy and cheep breeding under laboratory conditions, easy manipulation with gametes, embryos, adults; embryos develop outside the mother’s body, short life cycle, simple genom, … BI6140 EMBRYOLOGIE 9 alternativní popis obrázku chybí https://cs.wikipedia.org/wiki/Octomilka, https://cs.wikipedia.org/wiki/H%C3%A1%C4%8F%C3%A1tko_obecn%C3%A9 alternativní popis obrázku chybí BI6140 EMBRYOLOGIE 10 Basic terms § development = qualitative change § ontogenesis = development of the individual § phylogenesis = evolution of species § gamete = a mature germ cell § zygote = a fertilized egg § proliferation = cell division § cell growth = quantitative change, anabolism / catabolism> 1 § differentiation = cells change their functional or phenotypical type § migration = cell movement § morphogenesis = shape and structural development § association = moving cells into larger units § apoptosis = programmed cell death 11 BI6140EN EMBRYOLOGY Anatomical terms of location 12 BI6140EN EMBRYOLOGY https://static.wikia.nocookie.net/psychology/images/c/c2/Anatomical-directions.svg/revision/latest? cb=20070410223948, https://www.kenhub.com/en/library/anatomy/anatomical-terminology Anterior In front of or front Posterior In behind of or behind Ventral Towards the front of the body Dorsal Towards the back of the body Distal Away or farthest away from the trunk or the point of origin of the body part Proximal Closer or towards the trunk or the point of origin of the body part Median Midline of the body Medial Towards the median Lateral Away from median Superior Towards the top of the head Inferior Towards the feet Cranial Towards the head Caudal Towards the tail External Towards the surface, superficial Internal Away from the surface, deep Superficial Nearer to the surface Deep Farther from the surface Palmar Anterior hand or palm of hand (palmar) Dorsal (of hand) Posterior surface of hand (dorsum) Plantar Inferior surface of foot (sole) Dorsal (of foot) Superior surface of foot (dorsum Reproduction § basic property of living organisms § ability to form the basis of a system, which is the same as the founding system § allows to preserve the species and time continuity of life, to develop, increase the number of individuals, ensure the survival of the genetic lineages § sexual and asexual, or their alternation (metagenesis) § the level of reproduction is an indicator of the well-being of an organism in a given environment § an indicator of the balance of conditions in the external and internal environment of the organism § alternative definition by my colleague Aleš Bourek, Ph.D. J: male/man + female/woman + God/nature/fortune = offspring BI6140EN EMBRYOLOGY Reproductive system § system of reproductive organs (so-called generative organs) § glands + ducts (urogenital system) + accessory glands (yolk, endocrine, seminal vesicles in ♀, seminal vesicles in ♂) + copulatory organs + organs used for sexual selection (feathers, sounds, odor signals,…) § primitive reproductive organs can already be found in the phyllum Cnidaria Fertility: § basic biological property § a prerequisite for the time existence of the species § complex feature based on the ability to have healthy offsprings in the optimal number (in a given time period) § determined by a number of genes (polygenic inheritance) § heritability, (h2) of fertility indicators is low, fertility of animals is decided mainly by environmental conditions (eg. breeding conditions) § https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/PeackockSide.jpg/258px-PeackockSide.jpg https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/PeackockSide.jpg/258px-PeackockSide.jpg BI6140EN EMBRYOLOGY Asexual reproduction § x million species of animals exist on the Earth, but only about 1,000 of them reproduce asexually, in some species: (regular) alternation of sexual and asexual reproduction = metagenesis § offsprings are „genetic copies“ of a single parent § based on regeneration, mitosis (and its modifications) § in addition to mitosis, promitosis, multipolar mitosis, and multiple division of multinucleated cells can be observed § in unicellular and primitive multicellular organisms, leads to clones § somatic cells of the parent individual → somatic cells of offsprings § disadvantages: does not lead to genetic diversity among offsprings, but to genetic uniformity; → limited ability of offsprings to adapt § advantages: just one individual is needed for this type of reproduction, fast multiplication BI6140EN EMBRYOLOGY Mitosis and its modifications § endomitosis: shortened karyokinesis, the cell enters a modified prophase: chromosomes form and divide longitudinally in the nucleus, BUT the nucleus does not divide, the multiplied chromosomes despiralize, the nucleus enters the resting phase, → increased cell function, leads to polyploidy (increased number of chromosomes in the cell); back: somatic reduction § polytenia: chromatin synthesized in S phases is stored in so-called polytene chromosomes, in each S phase the number of chromosomes doubles, but there is no division into chromatids; →increases cell function - but does not lead to polyploidization, back: somatic reduction § somatic reduction: the cell enters a typical mitosis without previous S phase of the cell cycle § restitution division of the nucleus: after metaphase, telophase reconstruction of a single nucleus follows, the result: a cell with twice the number of chromosomes, in the parthenogenetic development of eggs, it adjusts the haploid state of the egg to diploid § promitosis (pseudomitosis): all karyokinetic phases inside the nucleus → a constriction; phylogenetic precursor of mitosis, especially in protozoa (formation of plasmodia - multinucleated cells): plasmodia are formed by repeated karyokinesis within a single cell (eg. spores), which may be followed by the breakdown of a multinucleated cell into mononuclear cells § multipolar mitosis: in eggs in polyspermia; however, chromosomes are not evenly distributed in daughter cells and development does not continue BI6140EN EMBRYOLOGY endomitosis = division of chromosomes without following nuclear division → increased number of chromosomes in the nucleus Sexual reproduction § combination of genetic material 2 organisms → genetically variable offsprings § chromosomes of two parents are segregated and recombined → no two offsprings are identical to each other or to either parent § relatively slow type of reproduction § external and internal fertilization § hologamy (the gametes are like ordinary cells, one cell org.) § oogamy (in multicellular, germ cells different from somatic cells) § gametic reduction (1n gametes, otherwise 2n phases) § zygotic reduction (2n only briefly for zygotes until the end of reduction division) § gonochorism: individuals have one sex of two distinct ones, males + females § hermaphrodism : an individual has both male and female reproductive organs § parthenogenesis: development of an individual from an unfertilized egg without male gamete (Insecta), sperm-based parthenogenesis is not known § heterogony: alteration of sexual and parthenogenetic reproduction (according to external conditions; Insecta) BI6140EN EMBRYOLOGY hermafrodismus: simultánní, geografický, sukcesní – proterogynie, proterandrie; division of chromosomes not followed by nuclear division that results in an increased number of chromosomes in the cell Oocyt má oocyt má zásobu všech typů RNA a může v průběhu dlouhé profáze syntetizovat proteiny z prekurzorů v cytolazmě Meiosis § the formation of gametes and accurate transfer of genetic material to them in sexually reproducing organisms § key event in eukaryotes; § ensures the same number of chromosomes in the offspring as in the parent organism § the first meiotic division separates pairs of homologous chromosomes to halve the chromosome number (2n → 1n), immediately followed by: § the second meiotic division - separates sister chromatids § disorders → serious consequences (see further) § https://www.youtube.com/watch?v=LUFYcqtMKf0 BI6140EN EMBRYOLOGY meiosis complex video meióza, nejčastější příčiny abortů: Turnerův s., trisomie 16, triploidie MEIOSIS I PROPHASE I http://facstaff.cbu.edu/~aross/embryo/meiosis/04leptotene.GIF http://facstaff.cbu.edu/~aross/embryo/meiosis/05zygotene.GIF Meiosis anonymus (2) BI6140EN EMBRYOLOGY MEIOSIS I PROPHASE I http://facstaff.cbu.edu/~aross/embryo/meiosis/06pachytene.GIF http://facstaff.cbu.edu/~aross/embryo/meiosis/07diplotene.GIF http://facstaff.cbu.edu/~aross/embryo/meiosis/08diakinesis.GIF Meiosis anonymus (3) BI6140EN EMBRYOLOGY § METAPHASE I: homologous chromosomes → equatorial plane, microtubules of the dividing spindle connected to the centromere kinetochores so that from each pole they always reach one of the homologous chromosomes § ANAPHASE I: separation of whole homologous chromosomes to opposite poles of the nucleus (reduction of the number of chromosomes), a set of chromosomes is collected at each pole (combination of maternal and paternal chromosomes, with recombinant chromatids due to crossing-over) § TELOPHASE I: terminated by cell division → two haploid cells § § MEIOTIC DIVISION II: except for the haploid number of chromosomes, it do not differ from mitosis Meiosis BI6140EN EMBRYOLOGY https://ib.bioninja.com.au/standard-level/topic-3-genetics/33-meiosis/crossing-over.html BI6140 EMBRYOLOGIE 22 https://ib.bioninja.com.au/standard-level/topic-3-genetics/33-meiosis/meiotic-division.html Meiosis Crossing over https://ib.bioninja.com.au/standard-level/topic-3-genetics/33-meiosis/crossing-over.html § No crossing-over (left): 4 gametes, due to the random segregation 2 gamets are always are identical to each other § Crossing-over occurs (right): 4 different recombinant gametes → separation of sister chromatids → 4different recombinant gametes Gametogenesis § development of primordial germ cells (extraembryonic origin) and their migration into the gonads, further development → mature gametes § most animals contain primordial germ cells → gametes § primitive animals: gametes arise from undifferentiated cells in tissues and transformation into gametes is due to external influences (eg. adverse conditions); special reproductive organs (e.g. in Porifera) are not differentiated; § in most cases, reproductive organs develop and produce germ cells (gametes, sperm, and eggs) and allow them to fuse in the zygote. Reproductive organs usually arise from the special germinal epithelium of the coelom wall. Primitive special reproductive organs can already be found in phyllum Cnidaria. BI6140EN EMBRYOLOGY Savčí typ (typ Drosophila) savci včetně člověka, někteří obojživelníci, plazi, většina řádů hmyzu a většina dvoudomých rostlin pohlaví: XX (homogametní) tvoří vajíčka pouze s chromozomem X (samice) pohlaví: XY (heterogametní) tvoří spermie buď s chromozomem X nebo s Y v poměru 1 : 1 (samci) Ptačí typ (typ Abraxas) ptáci, některé ryby, někteří obojživelníci a motýli pohlaví: ZW (samice) pohlaví: ZZ (samci) Gametogenesis § multiplicative phase: mitotic division of primordial oogonia and spermatogonia § growth phase: increasing the volume of the cytoplasm, formation of primary spermatocytes and oocytes § maturation phase: formation of haploid secondary spermatocytes and oocytes (1st meiotic division) § the second meiotic division produces haploid spermatids and an ovulated secondary oocyte, while spermatids must undergo another process of differentiation, so-called spermateliosis (the course depends on what type of sperm are produced, the most common type are with flagellum = tail), the oocyte is a mature egg cell after the second meiotic division § spermatogenesis → 4 mature spermatozoa § oogenesis → 1 mature oocyte and 3 polar bodies or 2 if the first polar body does not undergo cell division (as in humans) BI6140EN EMBRYOLOGY Savčí typ (typ Drosophila) savci včetně člověka, někteří obojživelníci, plazi, většina řádů hmyzu a většina dvoudomých rostlin pohlaví: XX (homogametní) tvoří vajíčka pouze s chromozomem X (samice) pohlaví: XY (heterogametní) tvoří spermie buď s chromozomem X nebo s Y v poměru 1 : 1 (samci) Ptačí typ (typ Abraxas) ptáci, některé ryby, někteří obojživelníci a motýli pohlaví: ZW (samice) pohlaví: ZZ (samci) Gametogenesis § includes development of germ cells (extraembryonic origin) and their migration into the gonads § further development according to different schemes for ♂ and ♀: a)mitotic germ cells proliferation in the germinal epithelium b)in humans, oogonia multiplie in ♀ by the end of the 5th month of pregnancy, up to 7 million germ cells are formed, then their loss (atresia) until menopause c)spermatogonia retain the ability to reproduce throughout life BI6140EN EMBRYOLOGY Savčí typ (typ Drosophila) savci včetně člověka, někteří obojživelníci, plazi, většina řádů hmyzu a většina dvoudomých rostlin pohlaví: XX (homogametní) tvoří vajíčka pouze s chromozomem X (samice) pohlaví: XY (heterogametní) tvoří spermie buď s chromozomem X nebo s Y v poměru 1 : 1 (samci) Ptačí typ (typ Abraxas) ptáci, některé ryby, někteří obojživelníci a motýli pohlaví: ZW (samice) pohlaví: ZZ (samci) Primordial germ cells (PGC) § → germ cells (gametes) § their isolation and cultivation → embryonic germ cells ("embryonic germ cells", EGCs, therapeutic potential) § = gonocytes, mitotic division → spermiogonia (spermatogonia) and oogonia § in the human embryo, they are detectable 24 days after fertilization in the area of the yolk sac, in week 4-6 they migrate (active movement ?, growth forces and directed proliferation?) to the genital region and become part of the germinal epithelium of the ovaries / testicles, → oogonia / spermatogonia § PGC in extragonadal areas → teratomas § the basics of human gonads acquire an M / F character at week 12: development determined by gonosomes, TDF ("testis-determining factor" on the short arm of the Y chromosome) and MIF (Müllerian inhibiting factor; produced by Sertoli cells) BI6140EN EMBRYOLOGY Spermatogenesis § spermatozoa: develop in the seminiferous tubules (type of tubular glands) from male primordial germ cells called spermatogonia § maturation begins under the influence of sex hormones in puberty § spermatogonia and further developmental stages of cells are connected by cytoplasmic bridges - synchronous development of a group of cells, initially dependent on Sertoli cells § Sertoli cells: → environment for development, a barrier regulating the exchange of molecules and protect against immunological destruction (blood-testis barrier, one of the tightest tissue barriers in the mammalian body, similar to blood-brain barrier ) § sperm production in men: development takes 64 days, attention!: eg. antibiotics, antimitotic treatment !!! § sperm belong to the smallest cells of the body BI6140EN EMBRYOLOGY Spermatogenesis § spermatogonia: on the basement membrane of the seminiferous tubules § → developmental stages of type A, IM and B. Type B leaves the basal compartment and enters the adluminal compartment between Sertoli cells → mitosis → 2 spermatocytes I. Thus, spermatogonia repeatedly divide (reproductive zone), enriched with nutrients and mitotically divided into spermatocytes I. We call this stage the growth stage. § when the cell enters the maturation stage, the first meiotic division occurs. Spermatocytes II are formed (prespermatids, relatively shortest period of existence within spermatogenesis). The second meiotic division produces spherical spermatids with haploid sets of chromosomes. Spermatocytogenesis is finished and spermiohistogenesis (spermateliosis) begins Junqueira a kol., 1997 BI6140EN EMBRYOLOGY Spermiohistogenesis § reduction of the nucleus: chromatin condensation § cytoplasm reduction: → residual bodies (phagocytosis by Sertoli cells) § condensation of the Golgi apparatus → acrosome: hyaluronidase, acrosin, proacrosin, collagenase § flagellum development: mitochondria spirally arranged in the proximal part in the tale § the cells are still connected by cytoplasmic bridges § http://www.embryology.ch/images/cimggametogen/03spermato/c3h_spermiogenese.gif anonymus (2) 1 Axonemal structure,first flagellar primordium 2 Golgi complex 3 Acrosomal vesicle 4 Pair of centrioles (distal and proximal) 5 Mitochondrion 6 Nucleus 7 Flagellar primordium 8 Microtubules 9 Sperm cells tail 10 Acrosomal cap BI6140EN EMBRYOLOGY Spermatozoa § mammalian sperm in the seminiferous tubules: only morphological maturity, immobile, incapable fertilization §by the fluid produced by tubules, spermatozoa enter the epididymis § biological maturation during transport in ♂ reproductive tract § in ♀ reproductive tract: capacitacion - changes in cytoplasmatic membrane, acquisition of fertilization ability § human sperm: movement 1 to 4 mm / min., few reserve substances, diffusion nutrition, limited life, calcium fundamentally affects functionality C:\Users\Nejezchleb\Desktop\Bailey005.jpg Sperm of different animals: A, B fish; C, D birds; E, F snakes; G Nematoda - Ascaris; H bats; K rodents; L newt; M, N, O, P crustaceans; u: undulating membrane Knoz J., 1979 BI6140EN EMBRYOLOGY Oocytes §ova (plural, lat.), ovum (singular, lat.) §unicellular formations that contain genetic information and nutrition material in the early stages of embryo development §spherical, with an asymmetric internal structure §during oogenesis, animal-vegetal polarity arises, the animal pole contains germinal vesicle; vegetal pole is rich in yolk §the amount of yolk (proteins, lipids and glycogen to nourish the embryo) correlates with the duration of development reguired before the individual can feed itself after hatching or before placental attachement with mother is established §the envelopes: membrana vitellina (vitelline envelope), albumen („egg white“), shell membranes, calcium shell; zona pellucida in mammals; §the plasma membrane of an egg is covered by a glycoprotein layer in mammals (=zona pellucida) and generally referred to as vitelline envelope which plays an important role in fertilization. Eggs deposited on land (reptiles, birds) have hard shells. Eg. the yolky chicken egg is surrounded initially by a vitelline envelope. Above this envelope, “egg white” (contains ovalbumin) is deposited + shell membranes are added. §quantity of yolk and its distribution in the eggs → different types of cleavage after fertilization § fertilization → holoblastic (total) cleavage (sea urchins, amphibians,…) → meroblastic (partial) cleavage (superficial; insects, disc-shaped in fish, reptiles and birds) §when an egg develops in the presence of follicular cells, the oocyte is surrounded by one or more layers of epithelially arranged cells that are not its sister cells. These are somatic cells form a follicle around the oocyte. We encounter this development, for example, in insects, reptiles, birds and mammals, incl. humans. BI6140EN EMBRYOLOGY https://onlinesciencenotes.com/wp-content/uploads/2021/05/sperm-and-egg-of-frog.jpg Eggs based on yolk quantity and its distribution §Holoblastic (oligolecithal) eggs a)alecithal: without yolk b)isolecithal: even distribution of yolk, total cleavage → equally large blastomeres, equal cleavage (mammals, echinoderms) c)heterolecithal: moderate yolk at vegetative pole (amphibians) §Meroblastic (polylecithal) eggs a)telolecithal: most vertebrates (fishes, reptiles, birds), yolk accumulated at the vegetative pole (heavier), the opposite animal pole contains the nucleus of the oocyte → inequal cleavage: animal pole → micromers, vegetative pole → macromers; special type: discoidal cleavage b)centrolecithal: arthropods, superficial cleavage c) Note: humans - oligolecithal, isolecithal oocytes, total and equal cleavage accordint to Knoz J., 1979 BI6140EN EMBRYOLOGY Oogenesis, folliculogenesis anonymus BI6140EN EMBRYOLOGY §oogenesis: the process by which female germ cells develop into mature eggs (ova) §folliculogenesis: is the process by which ovarian follicles develop from primordial to Graafian (mature) follicles, culminating in ovulation or atresia §primordial follicle §primary follicle §secondary follicle §tertiary (antral) follicle: contains an antrum (fluid-filled cavity), but it is not fully mature §Graafian follicle: mature/preovulatory follicle, the antrum is fully expanded, and the oocyte is surrounded by the cumulus oophorus (a cluster of granulosa cells), hormonal changes trigger the oocyte to complete meiosis I and prepare for release during ovulation § Oogenesis § maturation of the follicles continues only in and after puberty due to hormones § meiosis I → two haploid cells: one oocyte II and one polar body § meiosis II is initiated at the time of ovulation (in most mammals) and is completed only after the sperm penetrates the egg: oocyte II. → one egg and the second pole body are formed § all polar bodies are resorbed (this is generally the case, in humans the first polar body does not undergo division § Note: the picture shows (the largest) tertiary (antral) follicle § ovulation in uniparous animals: ovulation of a single egg (human, apes, elephants,…) § ovulation in multiparous animals: ovulation of more eggs (rodents, carnivores,…) § graafian follicle http://medcell.med.yale.edu/histology/ovary_follicle.php BI6140EN EMBRYOLOGY Oogenesis § ovulation is caused by LH peak → ovulated oocyte (human): limited lifespan (!), no reserve substances, diffuse nutrition, energy source: pyruvate, nucleic acid synthesis does not take place, but the oocyte contains them § in humans: at the beginning of the cycle a cohort of about 20 early antral follicles begins to evolve, but only about 3 reach Ø 8 mm → one of the growing follicles (most sensitive to gonadotropins) reaches ovulation as the so-called dominant follicle, the others undergo atresia (apoptosis) ) § AMH ("anti-Müllerian hormone"): important role in oocyte development - produced by granulosa cells of preantral and early antral follicles, its concentration correlates with ovarian reserve (diagnostic significance) § after ovulation: luteinization of granulosa cells → corpus luteum → progesterone (affects the differentiation of tissues of the reproductive system) § absence of fertilization: luteolysis (apoptosis) and collagenous degeneration of corpus luteum → corpus albicans § fertilization: hCG (human chorionic gonadotropin, produced by the syncytiotrophoblast blastocyst), hCG supports the activity of the corpus luteum graviditatis (produces progesterone especially in the first 2 months of pregnancy) BI6140EN EMBRYOLOGY Gametogenesis (meiosis) disorders §teratomas: tumors of partly unclear origin, possible explanation: they arise from primordial germ cells that have deviated from their migratory pathway §disorders of gametogenesis (meiosis) → chromosomal abnormalities (structural and numerical): a) aneuploidies (abnormalities in the number of chromosomes, usually trisomy or monosomy = there is an extra chromosome in the chromosome pair, or it is missing): • non-disjunction (= incorrect segregation) of the chromosome(s) during the 1st (2nd) meiotic division • incorrect (premature) sister chromatid separation during 1 meiotic division (dominant way?) • other causes: Spindle Assembly Checkpoint (SAC) permeability, spindle instability • Down s. (trisomy 21), Edwards s. (trisomy 18), Patau s. (trisomy 13), Klinefelter's s. (47, XXY, or 48, XXXY), Turner s. (45, X), triple syndrome X,…,often of maternal origin, age depend b) structural chromosomal abnormalities: translocation of a part of a chromosome to another (common for chromosomes 13, 14, 15, 21, 22); loss of a chromosomal part (cri-du-chat syndrome = cat scream syndrome = partial deletion of short arm of chromosome 5), inversion,… §gene mutations §more than 75% of miscarriages during the first 2 weeks and more than 60 % in the first trimester of pregnancy are caused by chromosomal abnormalities (the most common are 45, X (Turner syndrome), triploidy, trisomy 16). §chromosomal abnormalities cause 7% of congenital malformations and gene mutations another 8 % of congenital malformations BI6140EN EMBRYOLOGY Role of hormones in reproduction •Stress → increase in stress hormone levels (cortisol) → decrease in GnRH and increase in GnIH → decrease in sperm count / impaired ovulation,… anonymus (3) BI6140EN EMBRYOLOGY Coenorhabditis elegans § hermaphrodites + males § a pioneer in facilitating the study in the field of cell biology and genetics § model animal in infertility/fertility research § ameboid sperm § posterior pole is defined by the site of sperm entry into the unfertilized egg § 1st mitosis of the zygote is unequal → larger A daughter cell (AB), and a smaller P daughter cell (P1) BI6140 EMBRYOLOGIE 38 https://ars.els-cdn.com/content/image/1-s2.0-S1534580702002265-gr1.jpg https://ars.els-cdn.com/content/image/1-s2.0-S1095643322000101-ga1_lrg.jpg Drosophila melanogaster BI6140 EMBRYOLOGIE 39 § centrolecithal eggs in ovarioles § fertilization occurs only in the region of the oocyte which will become the anterior of the embryo § sperm are stored within the female’s body in a seminal receptacle and the paired spermathecae § egg chambre = multicellular structure in flies’ ovaries; in each a single egg is produced § egg chambre = internal cluster of germ cells comprised of 15 nurse cells and one oocyte, surrounded by an epithelial monolayer of somatic follicle cells § fertilization: internal; occurs after ovulation in the uterus § formation of A-P axis: maternal effect genes expressed in the ovaries → messenger RNAs that are placed in different regions of the egg → translation of these mRNAs after fertilisation: bicoid protein controls the production of anterior embryonic parts, nanos protein controls the formation of the posterior parts §D-V polarity: during oogenesis, the oocyte nucleus moves from a central posterior to an asymmetrical anterior position; nuclear movement = a symmetry-breaking step → A-P and D-V axes. The asymmetrically placed nucleus defines a region in the oocyte which accumulates high levels of gurken mRNA and protein; gurken = ovarian-specific member of TGF-α family of secreted ligands → concentration gradient → D-V gradient of EGF receptor activation in the follicle cells surrounding the oocyte. Cells | Free Full-Text | Murder on the Ovarian Express: A Tale of Non-Autonomous Cell Death in the Drosophila Ovary | HTML https://www.prirodovedci.cz/storage/images/800x600/5387.png HEAD HEAD Oocyte nucleus migration and dorsoventral axis formation. Schematic drawings of stage 7 oocytes (left) and mature eggs. Top: Wild type. The posterior-to-anterior movement of the oocyte nucleus forces the nucleus to acquire an asymmetrical position, which determines the dorsal side of the egg and establishes orthogonality between the AP and the DVaxes. Middle: If nuclear movement does not occur, AP and DVaxes are parallel to each other. Bottom: In binuclear oocytes, both nuclei move to the anterior pole to adopt random position at the anterior cortex. Both nuclei induce dorsal egg shell structures. Danio rerio § excellent model for human development § transparent embryos § telolecithal eggs: blastoderm + large amount of yolk § incomplete (meroblastic) cleavage § quick development § sperm with a tail piece § external fertilization § https://www.jove.com/v/5151/zebrafish-reproduction-and-development BI6140 EMBRYOLOGIE 40 Zebrafish take no time at all to develop--one of their many advantages as a model organism. A representative image showing sperm suspensions prepared in the present study are mainly composed of mature spermatozoa (1000 magnification). Xenopus laevis § large heterolecithal/mesolecithal oocytes ( >1 mm in diameter: a large nucleus/germinal vesicle (100,000 times larger than a nukleus in somatic cells, 1/3 of oocyte’s volume) § oocytes with synchronous cell cycle → large amounts of fertilized eggs can be obtained easily § a fully grown oocyte: 200,000 times as many ribosomes as an average somatic cell § arrested in MI until activation by progesterone → meiotic maturation of the oocytes § eggs surrounded by the vitelline membrane + jelly coating § sperm with a tail piece, 30 μm long § external fertilization BI6140 EMBRYOLOGIE 41 https://onlinesciencenotes.com/wp-content/uploads/2021/05/sperm-and-egg-of-frog.jpg The Physiology of the Xenopus laevis Ovary | SpringerLink Gallus gallus § one of the model amniote species for experimental embryology and development of the extraembryonic membranes § telolecithal eggs § recently ovulated egg: a preprimitive streak blastodisc + a large yolk mass; vitelline membrane; a large amount of albumen („egg white“) surrounds the vitelline membrane and is surrounded by the shell membrane and eggshell § internal fertilization BI6140 EMBRYOLOGIE 42 Chicken oviduct segments (A) and egg components (B). | Download Scientific Diagram Mus musculus § oligolecithal eggs (in eutherian mammals in general) § sperm with a tail piece § https://www.jove.com/v/5159/development-and-reproduction-of-the-laboratory-mouse § Monument to the laboratory mouse (bronze mouse knitting DNA, Памятник лабораторной мыши, Russia) BI6140 EMBRYOLOGIE 43 Pro lékařské pokusy zemřely miliony myší. V Rusku pro ně stojí pomník - ExtraStory www.wikipedie.cz Figure 1 from Why is chromosome segregation error in oocytes increased with maternal aging? | Semantic Scholar Summary Sperm (← spermatogenesis): § extremely small cells which lack most of their cytoplasm § ability to travel through an (internal or external) aquatic medium to reach the egg cell § flagellum to move toward the egg § all sperm consist of three basic pieces: the head (contains the genetic material and is capped by the acrosome (cap) (with enzymes needed for the sperm to penetrate the egg); the middle piece (with mitochondria that fuel the movements of the tail piece); the flagellum (tail piece) Eggs ( ← oogenesis): § designed for providing nutrients to the developing embryo § contains yolk (lipids, proteins, glycogen for embryo nutrition) § classified by the amount and the distribution of yolk in the egg § quantity of yolk and its distribution in the eggs → different types of cleavage after fertilization § the amounts of yolk are minimal in mammalian eggs, placenthal development is necessary for further embryo development § large eggs (birds, reptiles) have large amount of yolk to support embryonic development to advanced stages BI6140 EMBRYOLOGIE 44 Used and recommended literature F. Athar, N.M. Templeman. C. elegans as a model organism to study female reproductive health. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 2022; 266, 111152. L. W. Browder, C.A. Ericson, W.R. Jeffery. Developmental Biology. 3rd edition, 1991. ISBN 0-03013514-1. B. M. Carlson: Human embryology and developmental biology. 4th edition, 2009. ISBN 978-323-05385-3. G. German, T. Child. In vitro maturation of oocytes. In K. Coward & D. Wells (Eds.), Textbook of Clinical Embryology (pp. 300-312). 2013. Cambridge: Cambridge University Press. doi:10.1017/CBO9781139192736.031 R. Hodge: Developmental Biology : from a Cell to an Organism. 1st edition, 2010. ISBN 978-0-8160-6683-4. S. Horne-Badovinac . The Drosophila egg chamber-a new spin on how tissues elongate. Integr Comp Biol. 2014;54(4):667-676. doi:10.1093/icb/icu067 J. Knoz. Obecná zoologie. I Taxonomie, látkové složení, cytologie a histologie. II Organologie, rozmnožování, vývoj živočichů a základy biologie. PřF UJEP, Brno. 1979. L. C. Junqueira, J. Carneiro J, R. Kelly R. Základy histologie. 1997. ISBN 80-85787-37-7. R. Lüllmann-Rauch . Histologie. Překlad 3. vydání. Grada, Praha. 2012, 556 s. K. L. Moore, T. V.N Persaud: The developing human. Clinically oriented embryology. 8th edition, 2008. ISBN 978-0-8089-2387-9. S. Roth, J. Lynch. Symmetry Breaking During Drosophila Oogenesis. Cold Spring Harbor perspectives in biology. 2009. 1. a001891. 10.1101/cshperspect.a001891. J. M. W Slack: Essential developmental biology. 2nd edition, 2006. ISBN 978-4051-2216-0. Z. Vacek: Embryologie. 2006. ISBN 978 -80-247-1267-3. Z. Věžník: Repetitorium spermatologie a andrologie, metodiky spermatoanalýzy. Brno : Výzkumný ústav veterinárního lékařství, 2004. 1 sv. (různé stránkování). http://www.are.cz/data/file/gametogeneze_mitoza_a_meioza.pdf https://ib.bioninja.com.au/standard-level/topic-3-genetics/33-meiosis/stages-of-meiosis.html https://owlcation.com/stem/The-why-and-how-of-breeding-zebrafish-for-research https://sunlab.pnb.uconn.edu/research/ www.sci.muni.cz/ptacek https://link.springer.com/protocol/10.1007/978-1-59745-000-3_2 https://onlinesciencenotes.com/sequential-events-and-stages-in-the-development-of-frog-pre-embryon ic-embryonic-and-post-embryonic-development/ http://web.as.uky.edu/Biology/faculty/cooper/Population%20dynamics%20examples%20with%20fruit%20fli es/08Drosophila.pdf https://www.mdpi.com/2073-4409/10/6/1454/htm https://www.pacc.in/e-learning-portal/ec/admin/contents/60_BZO%2052_2020111502214594.pdf https://www.prirodovedci.cz/zeptejte-se-prirodovedcu/1696 https://www.researchgate.net/figure/General-structure-of-the-zebrafish-egg-The-zebrafish-egg-is-ap proximately-07mm-in_fig3_328858072 https://www.researchgate.net/figure/A-representative-image-showing-sperm-suspensions-prepared-in-t he-present-study-are-mainly_fig1_282244810 https://www.researchgate.net/figure/Non-passerine-a-and-Passerine-b-Spermatozoa-a-Non-passerines-F iliform-head_fig5_326827104 https://www.researchgate.net/figure/Chicken-oviduct-segments-A-and-egg-components-B_fig1_41110738 https://www.researchgate.net/figure/Germinal-vesicle-GV-transfer-a-GV-stage-mouse-oocyte-with-open ed-zona-b-GV_fig1_12355102 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/gallus-gallus https://www.shsu.edu/~bio_mlt/Chap5.html https://www.xenbase.org/anatomy/intro.do BI6140EN EMBRYOLOGY