Gastrulation to Neurulation 2 Flashcards
what gives rise to different mesoderm derivatives?
- depending on what signals cells receive when moving through PS in chick will give different mesodermal derivatives
- lateral mesoderm, intermediate mesoderm, paraxial mesoderm
paraxial mesoderm gives rise to what?
- head mesoderm
- somites –> which give rise to dermatome (dermis), sclerotome (cartilage)
and myotome (skeletal muscle)
intermediate mesoderm gives rise to what?
- kidneys
- gonads (called ovaries in women and testes in males)
lateral mesoderm gives rise to what?
- Splanchnic (circulatory system)
- Somatic (body cavity)
- Extra embryonic
what is the source of the signals that lead to the inducing and patterning of prospective mesoderm?
vegetal tissue induces mesoderm in animal cap
tissue recombination (experiment) tells us that vegetal tissue can induce mesoderm from “animal cap” ectoderm
dorsal vegetal cells induce what?
muscle and notocord from animal cap cells
ventral vegetal cells induce what?
blood and associated tissue from animal cap cells
explain the 3 signal model of mesoderm induction
- model describes interactions between different cells and signalling molecules that lead to differentiation of cells in mesoderm: vegetal, ventral and dorsal
- signals from vegetal region signalling up marginal zone
- signals from organizer signalling across mesodermal field: dorsal signals signalling across, ventral signals also signalling across
why are nodals more strongly expressed on the dorsal side?
because being induced by VegT, VG1 and B(eta)-Catenin
describe which molecules induce and pattern the prospective mesoderm
- VegT = TF expressed in vegetal cells –> induces expression of nodal-related signalling proteins (Xnrs) within same vegetal cells. Xnrs are a member of TGFβ family
- B-catenin = second messenger protein, active at high levels in dorso-vegetal regions -> increased B-catenin in these regions lead to enhances expression of Xnrs in those cells. B-catenin with VegT promotes activation of Xnr expression
- B-catenin also induces expression of, TF, siamois, this combined with high levels of Xnr signals induces “the organiser” in the dorsal region
- Organizer region sends signals that inhibit signalling of BMP (bone morphogenetic proteins) and create a gradient of Xnr signals. This combination of factors, including the inhibition of BMP and presence of Xnrs gradients plays a crucial role in providing different identities to the mesoderm cells
what are the main signalling molecules?
- sometimes they’ll need to be activated or inhibited
- BMPs and their inhibitors (e.g. chordin, follistatin, noggin)
- TGFβ, nodals, nodal related protein and their inhibitors (e.g. lefty, cerberus)
- Fibroblast growth factors
- Hedgehog factors
- Wnts and their inhibitors (e.g. sFRPs)
- Retinoic acid
- Notch/delta
VegT and Vg1 induce family signalling molecules: nodal (Xnrs), nodal expressed and secreted into animal region
where sperm enters becomes the ventral side of the embryo opposite side is dorsal, due to specification of the dorsal side B-catenin is expressed, B-ctaenin indues nodal in those cells
B-catenin also induces siamosis, required to induce organizer on dorsal side (organizer forms in dorsal mesoderm) is induced because of high level of Xnrs and expression of siamois - combination of both of these being expressed induces the organisaer in the dorsal mesodermmso organiser will secrete genes towards ventral side
the ventral side will pattern towards the dorsal side
ring of different mesoderm being induced
Endoderm derivates?
- trachea of lungs
- lining of digestive system (oesophagus, stomach, duodenum, small and large intestines)
- liver
- pancreas
describe which molecules induce and pattern prospective endoderm?
XENOPUS patterning of endoderm:
- Vg1 + VegT [maternal signals] ⟶ expressed vegetally, induce nodals in cell it’s expressed in - NOTE: tissues with high conc of nodal form endoderm / low conc of nodal ⟶ form mesoderm
- Xnrs [nodal related maternal and zygotic] ⟶ activates Sox17
- Sox17: switched on by nodals = induce endoderm
what are the ectoderm derivatives?
neural tube (spinal cord, brain, retina…) + outer layer (epidermic – hair, nails, lens, cornea…) +neural crest cells (form between neural and non-neural ectoderm)
VegT and Vg1 induce family signalling molecules: nodal (Xnrs), nodal expressed and secreted into animal region
where sperm enters becomes the ventral side of the embryo opposite side is dorsal, due to specification of the dorsal side B-catenin is expressed, B-ctaenin indues nodal in those cells
B-catenin also induces siamosis, required to induce organizer on dorsal side (organizer forms in dorsal mesoderm) is induced because of high level of Xnrs and expression of siamois - combination of both of these being expressed induces the organisaer in the dorsal mesodermmso organiser will secrete genes towards ventral side
the ventral side will pattern towards the dorsal side
ring of different mesoderm being induced
VegT and Vg1 induce family signalling molecules: nodal (Xnrs), nodal expressed and secreted into animal region
where sperm enters becomes the ventral side of the embryo opposite side is dorsal, due to specification of the dorsal side B-catenin is expressed, B-ctaenin indues nodal in those cells
B-catenin also induces siamosis, required to induce organizer on dorsal side (organizer forms in dorsal mesoderm) is induced because of high level of Xnrs and expression of siamois - combination of both of these being expressed induces the organisaer in the dorsal mesodermmso organiser will secrete genes towards ventral side
the ventral side will pattern towards the dorsal side
ring of different mesoderm being induced
describe which molecules induce and pattern prospective ectoderm?
- Instructive signals for ectoderm formation:
- instructive signals such as Foxi2 (maternal protein) and Fox1e - acts as TFs & activate the expression of Xema, which is required for ectodermal marker expression - Inhibitory Signals Prevent Ectoderm Formation at the Animal Pole:
- inhibitory signals, including Nodal and molecules like Ectodermin, Coco, and Norrin, counteract formation of ectoderm at the animal pole (stays in vegetal pole)
- these inhibitory signals prevent the instructive signals from reaching and initiating ectodermal development in animal pole
VegT and Vg1 induce family signalling molecules: nodal (Xnrs), nodal expressed and secreted into animal region
where sperm enters becomes the ventral side of the embryo opposite side is dorsal, due to specification of the dorsal side B-catenin is expressed, B-ctaenin indues nodal in those cells
B-catenin also induces siamosis, required to induce organizer on dorsal side (organizer forms in dorsal mesoderm) is induced because of high level of Xnrs and expression of siamois - combination of both of these being expressed induces the organisaer in the dorsal mesodermmso organiser will secrete genes towards ventral side
the ventral side will pattern towards the dorsal side
ring of different mesoderm being induced
describe which molecules induce and pattern prospective ectoderm?
- Instructive signals for ectoderm formation:
- instructive signals such as Foxi2 (maternal protein) and Fox1e - acts as TFs & activate the expression of (gene) Xema, which is required for ectodermal marker expression - Inhibitory Signals Prevent Ectoderm Formation at the Animal Pole:
- inhibitory signals, including Nodal and molecules like Ectodermin, Coco, and Norrin, counteract formation of ectoderm at the animal pole (stays in vegetal pole)
- these inhibitory signals prevent the instructive signals from reaching and initiating ectodermal development in animal pole
