Quiz 12/6 Flashcards
mesoderm segments
intermediate, axial, paraxial, and lateral plate
axial mesoderm becomes
notochord
intermediate mesoderm becomes
kidneys and gonads
paraxial mesoderm becomes
somites
lateral plate mesoderm becomes
circulatory system, body cavity, pelvis and limb bones
somites give rise to
sclerotome (vertebrae/cartilage), dermomyotome (skeletal muscle and back dermis)
what does the formation of somites result in?
segmentation of the vertebrate body plan where each vertebrae is a segment
formation of somites
occurs in pairs of right and lefts along the neural tube through EMT. Early somites can become any somatic cell, but once they go through EMT, they become committed to forming certain cell types (sclerotomes or dermomyotomes)specification of somites
specification of somites
gain identity through interactions with the surrounding neural tube, notochord, and ectoderm. sclerotomes form closest to the neural tube and dermomyotomes form from the remaining epithelial somites
signaling that specifies somites
initially, BMP gradient from ectoderm but notochord and somitic mesoderm express noggin to repress BMP signal, resulting in a gradient of BMPs. Somites come from low BMP levels (Foxc1/Foxc2), lateral mesoderm come from high BMP levels (Foxf1)
significance of Brachyury (T), Tbx6, and mesogenin
pioneer transcription factors for early specification of presomitic mesoderm, likely induced by Foxc1 and 2
when Tbx6 is lost from a somite
results in neural identity so somite becomes NT, mesoderm expresses neural markers Sox2 and Pax6, so Tbx6 likely represses neural markers
relationship between Mesogenin and Tbx6
mesogenin is upstream and necessary and sufficient for Tbx6 expression in presomitic mesoderm
what induces stem cells of caudal (posterior) progenitor zone to become either meso or ectoderm?
High anterior gradient of RA, which forms somites and neural plate. RA represses Fgf8 and Tbx6, resulting in neural fates. High posterior gradient of Fgf8 and Wnt from the tailbud represses RA through Cyp26b, resulting in mesodermal fates in the middle
how is early identity of somites along the trunk patterned?
Hox genes, more hox genes are posterior, fewer are anterior
somitogenesis
formation of somites, occurs one pair at a time with the first somites forming right behind the otic vesicle. Somites bud-off from the anterior portion of presomitic mesoderm
somite numbering
SI are most recently formed somites, S0 are somites being formed, and S-1 are the next somites to be made
Nueromesodermal progenitor cells (NMPs)
cells along the most posteriormost region of the tail that have the ability to become neural tube (Sox6) or paraxial mesoderm Tbx6)
where are NMPs found?
in the dorsal medial zone (DMZ), but eventually move posteriorly (collective migration) into the progenitor zone of the tailbud, reaching PSM
maturation zone
area that NMPs move through that results in them expressing mesodermal markers Tbx6 and mesogenin, as well as Cdc25 which allows for one cell division
main factors that drive axis elongation
cell proliferation, collective cell migration, and intertissue adhesion
regions of zebrafish tailbud
dorsal medial zone, progenitor zone, maturation zone, and emerging PSM zone
movements of neuromesodermal stem cells
start in the dorsal medial zone but then quickly collectively migrate into the progenitor zone where they slow and eventually migrate bilaterally into the maturation zones and then finally the PSM region
mesenchymal to epithelial transition (MET)
upregulation of mesodermal posterior (Mesp) codes for a Txfactor that regulates MET, Mesp is only expressed in the anterior half of the somite
role of Mesp
upregulates Eph in the anterior portion of the somites(S0) which triggers ephrin in the opposing posterior somite (S-1) and in the posterior half of it’s own somite
when do somites bud from the PSM
when posterior (ephrin) half separates from the anterior (eph) half, inducing epithelializaiton
Signaling of epithelialization
Cdc42 is inhibited by ephrin, which induces peripheral cells to become epithelial and surround mesenchymal somatic cell. Then, integrins are enhanced by eph-ephrin signaling which induces an ECM between the somites and promotes separation of somite SO from S-1
