Generating Cell Diversity in the Developing Nervous System

Question 1

Spinal Cord Differentiation

Answer 1

• differentiating neurons > outer layer of spinal cord in marginal zone (post-mitotic cells)
• dividing progenitors > inside layer, ventricular zone
• dorsal root ganglia > adjacent to spinal cord

Question 2

Sulcus Limitans Function

Answer 2

divides developing neural tube into dorsal alar plate and ventral basal plate - gives rise to sensory and motor areas of spinal cord and brainstem

Question 3

Morphogens

Answer 3

pattern tissue in a concentration dependent fashion
- SHH released from mesoderm and notochord > forms basal plate
- ectoderm adjacent to neural plate releases BMPs & Wnts > forms alar plate

Question 4

Holoprosencephaly

Answer 4

partial/complete failure of the prosencephalon to separate into the diencephalon & paired telencephalon vesicles
- caused by too little hedgehog signaling

Question 5

Cyclopia

Answer 5

extreme case of holoprosencephaly; single brain vesicle w/ large fused single midline eye

Question 6

Events that regulate the developing brain

Answer 6

Cell division & cell migration

Question 7

Contribution of the Cell Cycle

Answer 7

• dividing cells of developing NS are close to ventricular lumen, surrounded by the ependymal zone
• cleavage plan changes as neurogenesis proceeds (early > vertical plan > 2 symmetrical progenitors daughter cells), (late > horizontal > basal daughter = post mitotic neurons)

Question 8

Contribution of Cell Migration

Answer 8

histogenesis of the cerebral cortex
- new born neurons migrate along radial glial fiber supplied by neural progenitor > serves as scaffold that conducts new born neurons from ventricular region upward to accruing cortical layers

Question 9

Layered Structure of Cerebral Cortex

Answer 9

• 6 layers with unique expression code of transcription factors
• # of neurons varies bw species
• more cells = increased connections and complexity
• deeper layers born first; superficial layers have to migrate past deep layers upwards to accrue

Question 10

Tangential Migration

Answer 10

new born neurons arise from ganglionic eminence in the ventral striatum
- migrate long distances through the developing neocortex to supply inhibitory neurons

Question 11

Radial Migration

Answer 11

new born neurons arise at the ventricular surface
- migrate upwards in a radial pattern to form cortical pyramidal neurons (excitatory)

Question 12

Organization of forebrain, midbrain, and hindbrain

Answer 12

• forebrain > expression of transcription factors which presages formation of major brain divisions
• organizer region in the mid hindbrain junction expresses molecules and DNA binding transcription factors that specify adjacent regions

Question 13

Universal Genetic Mechanism for organizing the NS

Answer 13

• transcription factors turn on and off other genes
• hox genes are expressed in a nested pattern along the anterior posterior axis of the embryo
• organization of hox genes along chromosomes and their expression along body axis is conserved in all animals (evolution was key event)

Question 14

Developmental organization of hindbrain and cranial motor nuclei

Answer 14

• hindbrain composed of segregated rhombomeres numbered r1-r7 forming a line
• each segment defined by the expression of transcription factors including hox genes

Question 15

Neural Crest cells & Cranial Nerves

Answer 15

segmented nature for developing hindbrain imposes patterning to developing cranial nerves so they also form in segmented manner in facial region > consequence of neural crest cell migration from dorsal edge of hindbrain