mesoderm induction

Question 1

what is the antero-posterior axis

Answer 1

head to tail

Question 2

what is the dorso-ventral axis

Answer 2

back to belly

Question 3

left to right

Answer 3

more or less bilateral to symmetry

Question 4

in frog and fish what is the vegetal axis controlled by

Answer 4

maternal factors, the axis is already manifest in the unfertilised egg

Question 5

when is Vg1 protein produced

Answer 5

after fertilisation

Question 6

what are Vg1 and signalling protein Xwnt11 required for

Answer 6

establishment of dorso-ventral axis, early mesoderm formation and specification of dorsal character

Question 7

where is the mRNA of vegetally localised protein in Vg1

Answer 7

in the vegetal half of the egg, it becomes further restricted to vegetal cell cortex

Question 8

how is the dorsal ventral axis established

Answer 8

through sperm entry - this leads to cortical rotation

Question 9

what is cortical rotation

Answer 9

when the layer below the cell membrane shifts 30 degrees toward the future dorsal side, subcortical microtubules become reorientated with plus ends pointing away from the site of sperm entry this makes tracts for direct transport of proteins and mRNAs

Question 10

what does cortical rotation lead to

Answer 10

transport of vegetally localised molecules to future dorsal side - opposite to sperm point of entry

Question 11

what happens if cortical rotation fails

Answer 11

failure of the dorsal anterior stuctures

Question 12

what is the signalling centre in the dorsal vegetal region called and what is it required for in development

Answer 12

the Nieuwkoop centre is required for development of dorsal structures

Question 13

what happens when you transplant the Nieuwkoop centre

Answer 13

it induces the ectopic body axis and a twinned embryo will form with duplicated axis

Question 14

what does Wnt-B-catenin promote

Answer 14

formation of dorsal stuctures

Question 15

what ligand mediates signalling activities for dorsal character

Answer 15

Wnt

Question 16

what happens when Wnt ligand is stimulated

Answer 16

degradation of beta catenin is degraded which leads to the transduction of Wnt signalling to the nucleus where it regulates gene transcription factors of TCF family

Question 17

what happens if wnt or vg1 is misexpressed

Answer 17

2 embryonic axes containing dorsal structures form

Question 18

qwhat does the combined action of Wnt and other maternally derived signals lead to

Answer 18

the formation of the nieuwkoop centre in the dorsal vegetal region

Question 19

what is the chick equivalent of the nieuwkoop centre and what is it determined by

Answer 19

the posterior marginal zone - determined by gravity

Question 20

do maternal factors play are role in chick body axis establishment

Answer 20

no

Question 21

what does the formation of the posterior marginal zone lead to

Answer 21

it is the first symmetry break event in the chick blastoderm and provides signals that leads to the formation of the primitive streak - at the top of the streak is the organiser region (Henson’s node)

Question 22

how is the primitive streak induced in chick

Answer 22

it involves the removal of signals from the hypoblast that inhibit streak formation
the hypoblast must be replaced by the endoblast so streak formation can start

Question 23

what is a fate map used for

Answer 23

to understand how germ layers and their derivatives arise - it is important to know which cells give rise to the distinct cell types

Question 24

how are fate maps used

Answer 24

labelling of cells or single cells at an early stage during development to see what regions they develop into

Question 25

what determines cell types

Answer 25

signal factors

Question 26

what are fate maps of vertebrates

Answer 26

variations of basic body plans

Question 27

what info do fate maps not give you

Answer 27

the full potential of the cells or if they are commited

Question 28

what happens when the presumptive eye region is transplanted

Answer 28

an eye still develops as the cells are committed

Question 29

what signals specify the germ layers in frog embryo

Answer 29

induction takes place when one signal produced by a cell group promotes a change of fate in responding cells frogs mesoderm is induced in the ectoderm by signals from the vegetal region

Question 30

how is the mesoderm induced

Answer 30

in ectoderm cells by signals from the vegetal region

Question 31

what makes up the ectoderm

Answer 31

explants from the blastula stage of the embryo animal caps

Question 32

where are the mesoderm derivatives formed

Answer 32

cells from the marginal zone where the animal cap cells oppose the vegetal cells

Question 33

what does labelling explant confirm

Answer 33

if explant cells are labelled before combination with vegetal cells, it is shown they are needed for mesoderm

Question 34

what is the community effect

Answer 34

it ensure the development of all cells within an embryo, a critical number of cells are required for response to mesoderm inducing cells

Question 35

what is the cell fate indicated by

Answer 35

neighbouring cells

Question 36

when does mesoderm induction take place

Answer 36

within a competence period, the cells are able to be induced from the mesoderm for 7 hours 2 hrs of inducing signal during this period is sufficient for mesoderm formation

Question 37

what patterns the mesoderm

Answer 37

distinct inducing properties of dorsal and ventral vegetal cells dorsal vegetal cells induce muscle and notochord from animal cell caps

Question 38

what do dorsal vegetal cells induce

Answer 38

dorsal vegetal cells induce muscle and notochord from animal cell caps

Question 39

what do vegetal signals induce

Answer 39

the mesoderm, nieuwkoop centre and induction of the organiser

Question 40

what inhibits the patterning of the ventral mesoderm

Answer 40

signals from dorsally located organiser

Question 41

what inhibits mesoderm formation

Answer 41

blocking of signals through the TGFB receptors, leads to no mesoderm or axial structures

Question 42

what is the negative dominant approach to blocking signals through TGFB receptors

Answer 42

no signal from the mutant receptor even when dimerised with wild type receptor so mRNA encoding the mutant receptor is injected into both cells of a two cell embryo no mesoderm or axial structures form

Question 43

how does varying concentrations of activin affect expression and gene cohorts

Answer 43

genes expressed by ectodermal cells in response to increased conc of activin low = keratin med = Brachyury high = gooseloid organiser

Question 44

what does cells close to activin source express

Answer 44

gooseloid - cells far away express brachyury theres are transcription factors which regulate distinct target genes leading to differentiation of specific mesodermal cell types

Question 45

what happens when the organiser O in a chick is transplanted

Answer 45

it induces a new embryonic axis with patterned mesoderm and a nervous system

Question 46

what do grafts of an organiser produce

Answer 46

an additional body axis which contains neural tissue and a mesoderm

Question 47

what happens when bification of the signalling centre in early development occurs

Answer 47

2 primitive streaks are formed leading to twins which are not always fully formed