organiser Flashcards
what can al the organisers do and what is the exception?
all of the organisers with the exception o the mouse node can induce a full secondary body axis when transplanted into the epidermis
what is the general role of an organiser?
to organise the anterior-posterior axis and the dorsal ventral axis
why must patterning the neural structures be linked to the mesoderm and how is this achieved?
the brain and spinal cord must develop in sync with the muscle and spinal tissue- this occurs by the link in mesoderm and ectoderm development
what is the difference between transplanting a new organiser compared to an old?
if you transplant a new organiser you will get an entire axis and if you transplant an old one you will get more posterior axis
what patterns the anterior forebrain?
the anterior definitive endoderm in the xenopus, mouse and chick
what is expressed in the AVE, AME, anterior definitive endoderm in the xenopus, mouse and chick?
cerberus and hex and otx2
what does cerberus inhibit?
BMPs Wnts and Nodal
what does the transplant of mesoderm from along the AP axis show?
the more anterior mesoderm the more anterior ectoderm it can induce
what is the two step process in neural AP patterning?
the first activating signal is the mesoderm instructing all overlying ectoderm to be anterior neural. the second signal transforms part of this tissue that that it can acquire a more posterior identity.
what are the candidates for the first and second signals?
chordin and noggin are good candidates from the first activating signal and may act by inhibiting BMPS and Wnts. FGF and Wnt3a are candidates for posteriorising transforming signals.
what is the evidence for the primary and then secondary signalling process in the chick?
early node transplants will induce full nervous system whereas older ones will only induce more posterior ones
what has been implicated as an early neural inducer?
FGF - supported by chick experiments
what 5 things should an organiser be able to do?
the ability to become dorsal mesoderm (prechordal plate and chodamesoderm)
the ability to dorsalise the surrounding mesoderm into lateral moesderm (when it would otherwsie form ventral mesoderm)
the ability to dorsalise the ectoderm into neural ectoderm
the ability to cause the neural plate to become the neural tube
what does the shield form?
Like the amphibian dorsal blastopore lip, the embryonic shield forms the prechordal plate and the notochord of the developing embryo. The precursors of these two regions are responsible for inducing the ectoderm to become neural ectoderm. Moreover, the presumptive notochord and prechordal plate appear to do this in a manner very much like that of their homologous structures in amphibians.
how does RA act as a morphogen?
it acts in conjunction with FGF (it has been suggested they should deb considered a single morphogen system) along the AP axis to pattern. The mediate the expression of the box genes along the AP axis
