mesoderm induction Flashcards
what is the antero-posterior axis
head to tail
what is the dorso-ventral axis
back to belly
left to right
more or less bilateral to symmetry
in frog and fish what is the vegetal axis controlled by
maternal factors, the axis is already manifest in the unfertilised egg
when is Vg1 protein produced
after fertilisation
what are Vg1 and signalling protein Xwnt11 required for
establishment of dorso-ventral axis, early mesoderm formation and specification of dorsal character
where is the mRNA of vegetally localised protein in Vg1
in the vegetal half of the egg, it becomes further restricted to vegetal cell cortex
how is the dorsal ventral axis established
through sperm entry - this leads to cortical rotation
what is cortical rotation
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
what does cortical rotation lead to
transport of vegetally localised molecules to future dorsal side - opposite to sperm point of entry
what happens if cortical rotation fails
failure of the dorsal anterior stuctures
what is the signalling centre in the dorsal vegetal region called and what is it required for in development
the Nieuwkoop centre is required for development of dorsal structures
what happens when you transplant the Nieuwkoop centre
it induces the ectopic body axis and a twinned embryo will form with duplicated axis
what does Wnt-B-catenin promote
formation of dorsal stuctures
what ligand mediates signalling activities for dorsal character
Wnt
what happens when Wnt ligand is stimulated
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
what happens if wnt or vg1 is misexpressed
2 embryonic axes containing dorsal structures form
qwhat does the combined action of Wnt and other maternally derived signals lead to
the formation of the nieuwkoop centre in the dorsal vegetal region
what is the chick equivalent of the nieuwkoop centre and what is it determined by
the posterior marginal zone - determined by gravity
do maternal factors play are role in chick body axis establishment
no
what does the formation of the posterior marginal zone lead to
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)
how is the primitive streak induced in chick
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
what is a fate map used for
to understand how germ layers and their derivatives arise - it is important to know which cells give rise to the distinct cell types
how are fate maps used
labelling of cells or single cells at an early stage during development to see what regions they develop into
what determines cell types
signal factors
what are fate maps of vertebrates
variations of basic body plans
what info do fate maps not give you
the full potential of the cells or if they are commited
what happens when the presumptive eye region is transplanted
an eye still develops as the cells are committed
what signals specify the germ layers in frog embryo
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
how is the mesoderm induced
in ectoderm cells by signals from the vegetal region
what makes up the ectoderm
explants from the blastula stage of the embryo animal caps
where are the mesoderm derivatives formed
cells from the marginal zone where the animal cap cells oppose the vegetal cells
what does labelling explant confirm
if explant cells are labelled before combination with vegetal cells, it is shown they are needed for mesoderm
what is the community effect
it ensure the development of all cells within an embryo, a critical number of cells are required for response to mesoderm inducing cells
what is the cell fate indicated by
neighbouring cells
when does mesoderm induction take place
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
what patterns the mesoderm
distinct inducing properties of dorsal and ventral vegetal cells
dorsal vegetal cells induce muscle and notochord from animal cell caps
what do dorsal vegetal cells induce
dorsal vegetal cells induce muscle and notochord from animal cell caps
what do vegetal signals induce
the mesoderm, nieuwkoop centre and induction of the organiser
what inhibits the patterning of the ventral mesoderm
signals from dorsally located organiser
what inhibits mesoderm formation
blocking of signals through the TGFB receptors, leads to no mesoderm or axial structures
what is the negative dominant approach to blocking signals through TGFB receptors
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
how does varying concentrations of activin affect expression and gene cohorts
genes expressed by ectodermal cells in response to increased conc of activin
low = keratin
med = Brachyury
high = gooseloid organiser
what does cells close to activin source express
gooseloid - cells far away express brachyury
theres are transcription factors which regulate distinct target genes leading to differentiation of specific mesodermal cell types
what happens when the organiser O in a chick is transplanted
it induces a new embryonic axis with patterned mesoderm and a nervous system
what do grafts of an organiser produce
an additional body axis which contains neural tissue and a mesoderm
what happens when bification of the signalling centre in early development occurs
2 primitive streaks are formed leading to twins which are not always fully formed
