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Neurodevelopmental characterization of semaphorin 5B in C57Black mice Lett, Robyn Lynn Mwuese


The mammalian nervous system develops through five recognized stages: induction, differentiation, migration/axon guidance, synaptogenesis and pruning/apoptosis. Guidance cues, generally thought to be responsible for guiding axons through the developing organism, have been identified as playing additional roles in differentiation, directed cell migration, synaptogenesis, as well as pruning and apoptosis. Semaphorin 5B (Sema5B) is a member of the semaphorin family of guidance molecules; therefore, it is hypothesized that it is expressed in the developing nervous system of mice. This thesis has investigated the developmental expression pattern of Sema5B in C57Black mice by in situ hybridization, which demonstrated expression of Sema5B mRNA in four specific regions of focus: the spinal cord and associated dorsal root ganglia, the eye, the olfactory bulb and epithelium and the dorsal forebrain. In the spinal cord, Sema5B undergoes dynamic changes between E12 and E18 that are consistent with a potential role in the formation of laminar-specific targeting of sensory neurons within the dorsal horn. In the eye, expression of Sema5B is specific to the lens epithelium and the retinal ganglion cell (RGC) layer, which implies a role in either RGC differentiation, migration, or in the guidance of RGC axons to the optic disk. Expression of Sema5B by olfactory receptor neurons at E18 implies that expression may continue postnatally, thus indicating a potential role in the maintenance of the regenerative nature of the adult olfactory epithelium. Finally, expression of Sema5B in the ventricular zone and the cortical plate as it develops denotes a possible function of Sema5B in the differentiation and/or migration of neurons in the developing mouse forebrain.

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