AP Patterning Flashcards
gastrulation in amniotes and non amniotes
amphibian (non-amniotes) germ layers are specified before gastrulation
amniotes (chicks) germ layers specified during gastrulation
spemann & mangold 1924
dorsal blastopore lip (DBL) to ventral side causes a twinned embryo
DBL organises the surrounding tissue
what is the gastrula organiser in amniotes
henson’s node
organiser from early and late stages of gastrulation
early stage organiser - induces a full embryonic axis
late stage organiser - induces only trunk and tail
anterior and posterior organiser tissue
anterior organiser tissue forms anterior structures
posterior organsier tissue forms posterior structures
Nieuwkoop’s ectodermal grafting experiment 1952
implant ectodermal folds into neural tube during gastrulation
neural tissue requires posterior character (MB+HB)
2 models for AP patterning
1) activation - neural induction via BMP markers
2) transformation via posteriorisation
French Flag Model
act to specify >2 cell types
act at a distance
act directly on receiving cells
has to be required
gradient involved
Retinoic acid gain of function experiment (Degitz et al., 2003)
high RA dose - anterior truncation
RA not needed for overall AP patterning
MHB marker
FGF8
which morphogen is needed for posterior identity
wnt
kiecker et al., 2001
ectodermal implant (expresses either control gene/xWnt3a) into anterior neural tube
analyse mRNA in situ hybridisation for MB marker gene (En2) and Hb (Krox20)
wnt produces a mirror image pattern of HB and MB markers at a distance
what does the DBL contain
wnt inhibitors (Frzb1 & Dkk1) high anterior expression
loss of Dkk1 causes loss of anterior structures (headless embryo)
what is neuralation
neural plate to neural tube
MB rotation 180 degrees
Forms ectopic MB vesicles (tectum) and ectopic cerebellar structures
where is FGF8 expressed
between Otx2 (FB & MB marker) and Gbx2 (HB marker)
FGF8 soaked bead
ectopic tectum and cerebellum expression
example secondary organisers
FGF
BMP
WNT
Shh
HB structure
HB is a series of vesicles (rhomencephalon)
HB is segmented by rhombomeres (predict where cranial nerves form)
Fruit fly larvae segmentation
contain Hox genes
Ubx (ultrabithorax gene) form posterior ectopic set of wings
Wizenmann and Lumsden 1997
dissect, dissociate and fluorescently label chick rhombomeres
even = green odd = red
even-even number/odd-odd rhombomeres have good mixing (intermingle)
even-odd - less aggregation and do not mix well