AP Patterning

Question 1

gastrulation in amniotes and non amniotes

Answer 1

amphibian (non-amniotes) germ layers are specified before gastrulation
amniotes (chicks) germ layers specified during gastrulation

Question 2

spemann & mangold 1924

Answer 2

dorsal blastopore lip (DBL) to ventral side causes a twinned embryo
DBL organises the surrounding tissue

Question 3

what is the gastrula organiser in amniotes

Answer 3

henson’s node

Question 4

organiser from early and late stages of gastrulation

Answer 4

early stage organiser - induces a full embryonic axis
late stage organiser - induces only trunk and tail

Question 5

anterior and posterior organiser tissue

Answer 5

anterior organiser tissue forms anterior structures
posterior organsier tissue forms posterior structures

Question 6

Nieuwkoop’s ectodermal grafting experiment 1952

Answer 6

implant ectodermal folds into neural tube during gastrulation
neural tissue requires posterior character (MB+HB)

Question 7

2 models for AP patterning

Answer 7

1) activation - neural induction via BMP markers
2) transformation via posteriorisation

Question 8

French Flag Model

Answer 8

act to specify >2 cell types
act at a distance
act directly on receiving cells
has to be required
gradient involved

Question 9

Retinoic acid gain of function experiment (Degitz et al., 2003)

Answer 9

high RA dose - anterior truncation
RA not needed for overall AP patterning

Question 10

MHB marker

Answer 10

FGF8

Question 11

which morphogen is needed for posterior identity

Answer 11

wnt

Question 12

kiecker et al., 2001

Answer 12

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

Question 13

what does the DBL contain

Answer 13

wnt inhibitors (Frzb1 & Dkk1) high anterior expression
loss of Dkk1 causes loss of anterior structures (headless embryo)

Question 14

what is neuralation

Answer 14

neural plate to neural tube

Question 15

MB rotation 180 degrees

Answer 15

Forms ectopic MB vesicles (tectum) and ectopic cerebellar structures

Question 16

where is FGF8 expressed

Answer 16

between Otx2 (FB & MB marker) and Gbx2 (HB marker)

Question 17

FGF8 soaked bead

Answer 17

ectopic tectum and cerebellum expression

Question 18

example secondary organisers

Answer 18

FGF
BMP
WNT
Shh

Question 19

HB structure

Answer 19

HB is a series of vesicles (rhomencephalon)
HB is segmented by rhombomeres (predict where cranial nerves form)

Question 20

Fruit fly larvae segmentation

Answer 20

contain Hox genes
Ubx (ultrabithorax gene) form posterior ectopic set of wings

Question 21

Wizenmann and Lumsden 1997
dissect, dissociate and fluorescently label chick rhombomeres

Answer 21

even = green odd = red
even-even number/odd-odd rhombomeres have good mixing (intermingle)
even-odd - less aggregation and do not mix well