MATERNAL mRNA LOCALIZATION IN THE DEVELOPMENT
Putting RNAs at the right place in the right time





     GASTRULATION/NEURULATION
     ventral
     dorsal




ACCURACY AND REPRODUCIBILITY IN ACQUIRING THE CELLULAR FATE WITHIN THE EMBRYO



Differential mRNA localization to subcellular compartments
-allows for spatial regulation of gene expression
-essential for polarity set-up in oogenesis
-patterning during embryogenesis
-in Xenopus: localized maternal mRNAs generate developmental polarity along the animal/vegetal
axis.

CELL-TO-CELL SIGNALING vs. MATERNAL FACTORS IN TISSUE SPECIFICATION
Ectoderm and endoderm are specified by maternal factors in the egg Mesoderm is induced by vegetal
tissue
endoderm
mesoderm

MATERNAL vs. ZYGOTIC REGULATORS



VegT (T-box family transcription factor)
A – stage I oocytes
B – stage IV oocytes
C – ovulated egg
D – stage 9.5 embryo
E – stage 9.5 embryo
(vegetal pole view)
F – stage 10.25 embryo
(vegetal pole view)
G – stage 10.5 embryo
(vegetal view)
H – stage 12.5 embryo
(posterior view)
I- mid neural fold embryo (stage 16)

VegT RNA injection into vegetal/ventral blastomeres can induce secondary exis via induction of
dorsal fate…….
I – primary axis
II - secondary axis
nt – neural tube
nc – notorchord
green – muscles
arrow – ectopic auditory vesicles

………by activation of Xwnt8/b-catenin pathway



Squint – nodal-related morphogen important for establishment of dorsoventral axis



3’UTR is necessary and sufficient for Squint localization
     Sqt 3’UTRdel     b-globin UTR
     Sqt 3’UTRdel                   lacZ sqtUTR







Vg1 (TGFb family ligand)



Vg1 depletion by morpholinos delayes gastrulation and mesoderm induction with loss of head
structures, absence of notochord and fusion of somites (arrow)
chordin
cerberus

mesoderm markers
     mesoderm
Vg1
…..via loss of the induction of the mesodermal markers

MECHANISMS OF INTRACELLULAR mRNA SORTING
VLE - Vg1
SUK4- kinesin-1 heavy chain
total oocyte lysate

IgG – isotypic control
SUK2 –non-neutralizing Ab
SUK4 –neutralizing Ab
Vg1 mRNA localization

XKHC - kinesin 1
Red - injected Vg1 RNA
XKHC-T591 – rigor mutant (can not move – binds tight to microtubules)
XEg5-T105N – rigor mutant of kinesin unrelated to XKHC

KINESIN TRANSPORT









     Xcat2-RNP (early pathway gene)
     Vg1-Vg1RBP-XStau (late pathway gene)
     oocyte maturation
     ER
     ER TRAP (MC –mitochondial cloud)
 Vg1-Vg1RBP
polarized microtubules/kinesins
(transport over long distances - both late and early pathway genes hitch a ride)