Chapter 11: Formation of Axes Continued Part 2 Flashcards
The ectoderm is induced to become EPIDERMAL TISSUE by binding BMPS:
BMP4, BMP2, BMP7, ADMP. Nervous tissue forms in regions of the ectoderm that is protected from BMPS.
The organizer forms neural tube and neural tissue from the ectoderm by blocking ___.
by blocking BMPS that are otherwise working on the ectoderm to become neural tissue.
although BMPS are initially equally distributed throughout the ectodermal and mesodermal regions of a late blastula, during gastrulation, ____ and other transcription factors induced by twin and siamois (involved with organizer) inhibit transcription of BMPS in the dorsal region of the embryo.
BMPS inihibit genes involved in neural tissue formatin (ie/ inhibits ____, __, ___) and activates those involved in epidermal specification. HOW DOES BMP FUNCTION AS A GRADIENT?
the organizer in the dorsal region inhibits BMPS by releasing ___, __ and ___, which are activated by Smad2, Siamois, and Twin.
goosecoid (in prechordal plate mesoderm)
BMPS inihibit genes involved in neural tissue formatin (ie/ inhibits SOX3, FOXD4, NEUROGENIN) and activates those involved in epidermal specification.
NO BMP4 ON DORSAL SIDE (ORAGNIZER SIDE) INDUCES DORSAL MESODERM
- moderate levels of BMP4 induces intermediate mesoderm
- high levels of BMP4 induces ventral mesoderm
the organizer in the dorsal region inhibits BMPS by releasing NOGGIN, CHORDIN, AND FOLLISTATIN, which are activated by Smad3, Siamois, and Twin.
in addition to Noggin, Chordinand Follistatin, another inhibitor named ___ is within the ANIMAL HEMISPHERE THAT PREVENTS INTERFERENCE WITH DORSAL ECTODERM SPECIFICATION.
Norrin
Noggin is induced in the organizer due to twin,siamois and Smad 2. What 2 functions does noggin accomplish?
1) induces dorsal ectoderm to form neural tissue
2) dorsalizes mesoderm that would otherwise form the ventral mesoderm structures.
Chordin is induced in the organizer due to twin,siamois and Smad 2. What functions does it accomplish?
chordin is activated by betactatenin in the dorsal regions. It binds directly to BMP4 and Bmp2 and prevents their complexing with their receptors.
Follistatin is induced in the organizer due to twin,siamois and Smad 2. What functions does it accomplish?
- also secreted by the organizer on dorsal side. It is transcribed in the dorsal blastopore lip and notochord. Follistatin inhibits activin and BMPs, causing ectoderm to become neural tissue.
the neural region of the amphibian embryo is the area with ___ amount of BMPS
lowest amounts. High BMPS result in epidermis.
the dorsal-ventral axis is dependent on beta catenin organizer actions. The anterior posterior axis is predicted by a __ gradient. Explain
The anterior posterior axis is predicted by a Wnt gradient.
- The head region has the LOWEST WNT. The endomesodermal tissue (leading edge of dorsal blastopore lip, the most anterior part of the organizer aka pharyngeal endoderm) induces the most anterior head structures and block Wnt and BMP pathways. This is due to vegetal cells releasing Nodal and Vg1, inducing high amounts of Smad2 and Wnt antagonizing proteins like CEREBRUS. CEREBRUS is secreted by pharyngeal endomesoderm cells and inhibits BMPS, nodal related proteins and Wnt 8 to allow for proper head formation.
in addition to cerebrus, Frzb, dikkopf, Tiki, and notum also block Wnt signalling in order to induce a head.
in addition to cerebrus, ___ ,___ ,___ and __- also block Wnt signalling in order to induce a head. Which molecules block BMP? which ones block Wnt?
in addition to cerebrus, Frzb, dikkopf, Tiki, and notum also block Wnt signalling in order to induce a head.
- Pharyngeal endoderm secretes Dickkopf, Frzb, Cerberus, Tiki and IGF
- Dickkopf, Frzb, Tiki inhibit Wnt
- Cerberus inhibits Wnts and BMPs
•Prechordal plate secretes Dickkopf, Frzb and Tiki (Wnt inhibitors) and Noggin and Chordin (BMP inhibitors)
•Notochord secretes BMP blockers only (Chordin, Noggin, Follistatin)
•Insulin-like growth factor (IGF) likely serves as an adjunct between notochord and prechordal mesoderm
HIGH LEVELS OF WNT AND BMP are in the tail region because there are no inhibitors.
Name Wnt inhibitors of the organizer/prechordal mesoderm and pharyngeal endoderm
Dickkopf, Frzb and Tiki are Wnt inhibitors
Noggin and Chordin and follistatin are BMP inhibitors
How is left and right axis specified? Which gene (and thus protein) is expressed?
expression of Nodal gene (or Xnr1 in amphibians) in the lateral plate mesoderm on the LEFT SIDE OF THE EMBRYO determines left right axial formation. This is important for heart positioning and gut coding.
PITX2 (ONLY ON LEFT SIDE OF EMBRYO) and nodal also control right-left patterning.
Deposition is controlled by cytoskeleton during first cleavage events.
- cytoskeletal tubulin keeps Pitx2 and nodal on the left side.
- if ciliar movement in the organizer region is blocked, Xnr1 expression DECREASES, and there iwll be defects in the lateral assignment.
THe role of FGF and IGFs in preventing BMP and Wnt signalling for Neural induction instead
FGF and IGFs induce brain and sensory placodes. Placodes are thickenings of epithelium in the embryonic head ectoderm layer that gives rise to neurons and other structures of the sensory nervous system.
- Both FGFs and IGFs initiate RTK signal transduction cascade, which interfere with both BMPs and Wnt
