Date on Master's Thesis/Doctoral Dissertation

5-2010

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Anatomical Sciences and Neurobiology

Committee Chair

Mower, George D.

Author's Keywords

Visual cortex; Cortical plasticity

Subject

Visual cortex--Growth--Genetic aspects

Abstract

The goals of this dissertation is to further the understanding of the roles of two genes identified by differential display polymerase chain reaction (ddPCR) of cat visual cortex as candidate genes to play a role in visual cortical plasticity. Analysis of normal and dark rearing of cats at five and twenty weeks identified Dab-1, the mammalian homologue of the disabled-1 gene found in drosophila and Munc13-3, the mammalian homologue of the c. elegans "uncoordinated" or unc -13 gene. Dab-1 transcription analysis showed a pattern of high levels during the peak (5 weeks) and low levels at the nadir (20 weeks) of the critical period in normally reared animals with opposite transcription levels in dark reared animals (the "plasticity" pattern). Munc13-3 showed the opposite pattern with low levels of transcription at the peak of the critical period and high levels at the nadir in normally reared and opposite pattern in dark reared animals ("anti-plasticity" patterm). This project extended the mRNA findings on Western blot analysis to study protein expression of both genes in the visual cortex during the critical period in both cats and mice. This analysis confirmed both Dab-1 and Munc13-3 as candidate plasticity genes showing "plasticity" and "anti-plasticity" patterns of protein expression, respectively, in visual cortex. Immunohistochemical labeling of Dab-1 in cat visual cortex revealed a consistent developmental decline in density of immunopositive cells across all cortical lamina from birth through the critical period. Comparisons of Dab-1 immunohistochemistry in normal and dark reared cats at the peak and nadir of the critical period showed staining patterns consistent with the results of the total protein expression studies. There was a greater immunopositive cell density in normal vs. dark reared animals at the peak of the critical period and greater cell density in dark reared than normal at the nadir of the critical period. Through the use of genetic mutants lacking the Dab-1 gene, additional Western blot analyses were performed to assess potential relationships between Dab-1 and expression of NMDA receptor subunits during the visual critical period. An inverse relationship was found between mutant and wild-type mice in the ratio of expression of NR2A and NR2B subunits between normal and dark-reared animals indicating a strong relationship between the proteins. While future experiments need to be conducted to further elucidate more details on the specific functions of both genes, this research provides substantial evidence that Munc13-3 and Dab-1 are both genes with significant roles in the critical period of visual cortical development.

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