Lecture 6

Lecture 6 - Lecture 6 Determination and Differentiation:...

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Unformatted text preview: Lecture 6 Determination and Differentiation: Vertebrate nervous systems Previously Lateral inhibition by Notch-Delta interaction leads to neural fate determination among a group of cells that have equal potency. Intrinsic mechanism: cell-lineage based, asymmetric cell division and segregation of cellular determinants control neural fate specification. Extrinsic mechanism: non-cell lineage based, inductive interactions control retinal neuron fate in compound eye development. How are neural fate determined in vertebrate nervous systems? Cerebral cortex: competence Retina: inductive interaction Spinal cord: SHH gradient Neural crest: target-derived inducer Glial vs neuron: Proneural genes and neurogenic genes are conserved in vertebrate nervous system--Vertebrates have homologs of Drosophila proneural genes; For each Drosophila bHLH gene, Vertebrates have several members. e.g Mash-1 (for Mammlian ASC Homolog-1), neuroD, neurogenin, hes--Vertebrates bHLH genes promotes neural fate --Vertebrates have multiple genes that are homologous to Notch and Delta. --Vertebrates Notch and Delta genes function through lateral Inhibition to inhibit neuron formation from the progenitor cells. Vertebrate proneural genes regulate neurogenesis Fig. 3.13 DNS Overexpression of bHLH protein neuroD in frog embryos leads to excess neurons Fig. 1.31 DNS Competence what makes cells of each cortical layer distinct? Cortical layers Layer 5/6 - send axons to subcortical areas Layer 4 - interneurons Layer 2/3-send axons to other cortical layers 5/6 4 2/3 5/6 5/6 4 youngold Birthdating -- Thymidine labeling 3H-Thymidine is incorporated into DNA during S-phase of the dividing cortical cells in the embryo Brain of the pup is collected and sectioned, and 3H- Thymidine is visualized with autoradiography (Sidman, 1960) Fig. 3.7 DNS Transplantation experiment I-birthdating cortical neurons;-then transplant young neurons to VZ of older cortex; Observation: - Transplanted young neurons end up at superficial layer (layer II, III), like the neighbor cells Conclusion:-Young neuron fate is not determined. Fig. 4.19 DNS The transplantation experiments - II-transplant old neurons to VZ of young cortex; Observation:-Transplanted cells end up at...
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Lecture 6 - Lecture 6 Determination and Differentiation:...

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