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BIOL 302
Catherine Studholme

1 1. What are the relationships between epiblast, ectoderm and epidermis? When are they specified during mammalian development? - Epiblast > ectoderm > epidermis - Epiblast – one of the layers in laminal disk that give rise to embryo proper  Forms ectoderm  Made by inner cell mass  Split by small clefts that combine to separate embryonic epiblast from amniotic ectoderm - Ectoderm – specification during beginning of blastulation, gastrulation o Originate from embryonic epiblast - Epidermis – outer epithelial layer of embryo, derived from ectoderm 2. Which tissues are developing from ectoderm? - Surface ectoderm, neural crest, neural tube 3. What are the four stages in the formation of neuroblast from a blastula cell? 1. Competence/induction – cells become neuroblast if exposed to right combination of signals to become competent (conditional specification) 2. Specification – progression along neural differentiation pathway can be repressed by signals even after becoming competent 3. Determination (commitment) – neuroblast enter neural differentiation pathway and will become neuron even in presence of inhibitory signals 4. Differentiation – neuroblast leave mitotic cycle and express neuron genes 2 4. What is the neural plate and how is it formed? Why did we talk (again) about Spemann’s organizer transplant experiment in this context? a. Formation of neural plate – dorsal ectoderm thickens, mesoderm and pharyngeal endoderm signal cells in ectoderm to elongate into columnar neural plate cells i. Ectodermal cells transformed into specialized nervous tissue cells via morphogens from mesoderm (induction, competence) b. Neural plate – first sign of a nervous system, specified to become neural ectoderm?, becomes neural tube c. Spemann’s organizer transplant experiment – excise region above blastopore lip and put into ventral side of a host nd i. Cause host embryo to develop secondary dorsal axis and 2 dorsal blastopore lip 1. Transplant altered fate of overlying cells (influenced to develop into neural parts) ii. Organizer able to induce gastrulation and 2 neural plate 5. Explain inhibition as a regulatory mechanism during development. Give two examples (one could be d-v specification in Drosophila; go back and check). -inhibition of inhibition Example – BMP and its inhibitors - BMP expressed ventrally to induce ectoderm to become epidermis - Dorsal Organizer release inhibitor of BMP (noggin, chortin) to block effects of BMP to allow neural tissue to form o Without inhibitor only epidermis would form Example – Drosophila dorsal-ventral specification - D-V specification by dorsal and gurken - Dorsal transcription factor induce genes for ventralization, inihibits genes for dorsalization o Amount dorsal determine % dorsalization or ventralization 3 6. Define neurulation. List four stages of primary neurulation in chick embryo. - Neurulation = cells from the neural plate form the neural tube, embryo known as neurula during this process o Two ways of occurring – primary and secondary neurulation (birds and mammal specific) - Steps of primary neurulation in chick embryo 1. Formation of neural plate through shaping and folding 2. Shaping of neural plate through elevation 3. Bending of neural plate to form groove through convergence 4. Neural groove form neural tube via closure 7. What is happening with the neural plate cells during neurulation? - Neural plate cells will deepen to form neural tube which will close up 1. Shape, fold, elevate, converge to become neural groove 2. Columnarization – microtubules within cells elongate to columnar shape -> 3. Wedging – apical actin filaments constrict which narrow apical area of cells -> 8. What is the role of hinge points during neurulation? P337 text - The medial hinge point cells and dorsolateral hinge points help the neural plate bend to form the neural tube 1. MHP anchor to notochord and Change shape 2. Dorsolateral hinge points become wedge shaped to help convergence of neural fold to neural groove 3. Both hinges are induced to become wedge shaped to act as pivot that direct rotation of cells around it 9. What are the two major proteins which force the detachment of the neural tube from the surface ectoderm? (When did we mention e-cadherin before? Check blastocyst formation) - Cadherin 1. Neural tube express E-cadherin 2. Neural tube AND groove express isoform N-cadherin 4  Production of this isoform reduces binding affinity b/w neural tube and surface ectoderm - FLASHBACK = E-cadherin (in mammals) 1. Adhesion molecule aiding compaction in mouse embryo of blastomeres to form compact ball 10.What is the difference between primary and secondary neurulation? - Neurulation = formation of neural tube from neural plate - Primary neurulation – occur in anterior human, chick embryo 1. Shaping and folding = form neural plate 2. Elevation = shape neural plate 3. Convergence – bend the neural plate to form neural groove 4. Closure – close neural groove to form neural tube - Secondary neurulation – condensation (coalescing) of mesenchymal cells 1. Mesenchymal cells form medullary cord that becomes hollow to form neural tube 2. Occur in posterior embryo of chicken and human 11.What are the three primary vesicles formed during early brain development? Five secondary vesicles? 12.Where and how is the occlusion of the neural tube formed? What is the outcome of the temporary occlusion? P343 textbook - Early brain form occlusion of neural tube to increase brain cavity size without increasing cell number - Occlusion occur at interface of presumptive brain and spinal cord - Build up of positive fluid pressure - Neural folds close region between presumptive brain and spinal cord - Surrounding tissue dorsal tissue push inward to constrict neural tube at base of brain - Outcome = separate presumptive brain region from future spinal cord to allow build up of fluid pressure to increase cavity size 1. Allow expansion of future brain region 5 13.What are the two major paracrine factors involved in dorso-ventral polarization of the neural tube? Where do they originate from? How do they establish d-v axis? - Both are primary transcription factors that vary their concentration to differentiate dorsal from ventral - Sonic Hedgehog 1. Originate from notochord 2. Induce medial hinge cells to become
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