BCS/NSC 249 Developmental Neurobiology Mary Wines-Samuelson Email: mary_wines-samuelson@urmc.rochester.edu Textbook: Development of the Nervous System Sanes, Reh, and Harris Lectures on Blackboard; non-textbook reading materials

NSC 249--first third Jan. 18: Course overview and a discussion of gene regulation as it applies to neural development (MWS) Jan. 23: Neural induction and regionalization I (MWS) Jan. 25: Neural induction and regionalization II (MWS) Jan. 30: Neurogenesis, migration and differentiation in the nervous system I (MWS) Feb. 1: Neurogenesis, migration and differentiation in the nervous system II (MWS) Feb. 6: Neurogenesis, migration and differentiation in the nervous system III (MWS) Feb. 8: Regulation of neurogenesis in primate brain (Dr. David Kornack) Feb. 13: Neurite outgrowth and pathfinding I (MWS) Feb. 15: Neurite outgrowth II (MWS) end of material for Exam I Feb. 20: EXAM I

The origins of developmental biology -Hippocrates in 5th cent BC: “heat, wetness, solidification” -Aristotle in 4th cent BC: How are different parts formed? a) Preformationism b) Epigenesis (“upon formation”), or progression of new structures *This debate lasted for 1400 years! FINALLY… cell theory developed (1820-1880) Schleden (botanist) & Schwann (physiologist): All living things are derived from cells

Homunculus in sperm head (1694)  Early debates regarding development centered on preformationism vs. epigenesis Homunculus in sperm head (1694)  Early debates regarding development centered on preformationism vs. epigenesis

Weismann’s mosaic theory Radical idea: germ cells determine embryo characteristics (somatic vs. germline) -believed that nuclei divided asymmetrically to give rise to lineages with different cell fates… New debate! *a botanist monk would show that chromosomes determine inheritance of traits (Boveri & Sutton) The cell theory made preformationism untenable and the debate switched to how cells become specialized

Initial experiment by Roux appeared to support the mosaic model -”killed” one blastomere  half-embryo; thus, critical fate determinants missing

Later work by Dreisch was inconsistent with mosaic model *1st demonstration of regulation: embryo’s ability to develop normally despite missing or rearranged parts

*Development = a progression of fate restrictions? Repression of genetic expression can be reversed by changing the cytoplasmic environment ----- Meeting Notes (1/14/15 13:46) ----- *Thus, development must also involve some ability of cells to respond to a new context= plasticity (or adaptability) *Development = a progression of fate restrictions?

Fate restriction over time during brain development

Correct spatial and temporal control of gene expression and protein synthesis is essential during development

Genes are turned on/off by protein complexes bound to promoter Transcription requires: 1) open chromatin conformation state; 2) TATA box for RNA polymerase; 3) activators binding to enhancer elements in the 5’ UTR; and 4) RNA polymerase.

Regulatory regions (promoters) determine tissue-specific gene expression -mouse transgene with GH (pituitary) under the control of the mouse elastase gene (in pancreas) turns on GH in pancreas

Neural fate determination via: a) extrinsic signal, b) autocrine/paracrine signal, c) receptor-mediated signal transduction, & d) intrinsic determinant

Sequestration of signaling factors determines fate after mitosis

Mechanisms of cell fate determination A: Proximity to external signal source; B: activation of autocrine/paracrine signaling via endocrine gland; C: signaling via activation of receptor/signaling cascade; D: intrinsic signal coupled with controlled mitosis

Direct cell-cell (lateral) signaling can occur by: Diffusible ligand-receptor interaction Transmembrane ligand-receptor interaction Direct diffusion of factors across gap junctions

*estrogen/tamoxifen-ER: used to generate inducible transgenics Glucocorticoid receptor binding to hormone activates nuclear translocation & transcription Another example: estrogen/ER. We utilize this system to make inducible transgenic animals. Chap 9 Wolpert *estrogen/tamoxifen-ER: used to generate inducible transgenics

Another level of control: one TF (gene) can activate or repress other genes, depending on promoter context Chap.9 Wolpert

One mode of maintaining gene activation: positive autoregulation Fig 9.8: Continued expression of gene regulatory proteins maintains a pattern of gene activity

Inducing signals and competent tissue present during gastrulation *results are time-sensitive!

Heritability: the proportion of phenotypic variance due to genetic variance P= G + E; h2= genotypic variance/phenotypic variance (or g + e)

Localized determinants and asymmetric cell divisions establish the body plan of the early embryo

Gastrulation initiates at the blastopore (posterior), & extends anteriorly

Neural crest arises from the dorsal seam of the newly-formed neural tube Neural crest migration requires disruption of the basement membrane around the neural tube (to release the cells), as well as downregulation of their cadherins (adhesion proteins). Neural crest migrating over the somites will become sensory nerves and the autonomic nervous system; neural crest migrating dorsally will give rise to pigmented cells.

Mesoderm induces neural signaling in ectoderm; default is epidermis

Spemann and Mangold implicate the dorsal lip of the blastopore in neural induction