Expression and functional analysis of SOX3 in murine neurogenesis.

Abstract

The Sox (SRY-related HMG box) family of proteins are transcription factors. There are, in total, 30 different genes in the Sox family. Each Sox protein contains a HMG box (high-mobility-group) which functions as a DNA binding domain. The HMG box is highly conserved (>50% identity) throughout the entire Sox family. Sox3 belongs to the SoxB1 subgroup. SOX3 has been associated with human CNS related disorders. Duplication and mutations of SOX3 have been identified in patients with X-linked hypopituitarism (XH). Afflicted XH patients suffer from varying levels of mental retardation and pituitary hormone deficiencies which can lead to short stature. Previous studies have shown that Sox3 is expressed in nascent neuroprogenitor cells and is functionally required in mammals for development of the dorsal telencephalon and hypothalamus. Using a SOX3-specific antibody, data within my thesis shows that murine SOX3 expression is maintained throughout telencephalic neurogenesis and is restricted to progenitor cells with neuroepithelial and radial glial morphologies. In addition, characterisation of SOX3 expression within the adult neurogenic regions indicates that it is a lifelong marker of neuroprogenitor cells. In contrast to the telencephalon, Sox3 expression within the developing hypothalamus is up-regulated in developing neurons and is maintained in a subset of differentiated hypothalamic cells through to adulthood. In addition, using genome wide expression analysis examining a Sox3 null neural progenitor population, I identified a number of putative Sox3 targets. The data identified Dbx1 as a robust Sox3 target with Dbx1 down-regulation, at both the mRNA and Protein level, within Sox3 null mice at early stages of CNS development. I also independently confirm a number of SOX3 binding sites surrounding Dbx1, with one site showing clear enrichment in vivo. In addition, correlation between these putative targets and that of a previously published SOX3-ChIP data set show a clear enrichment for SOXB1 binding sites near the mis-regulated genes suggesting they are direct targets of Sox3. Taken together, data presented within my thesis identifies new regions of Sox3 expression and putative Sox3 targets. This data helps advance our knowledge of Sox3 regulation and function within CNS development.