Deciphering the Transcriptional Mechanisms and Function of SOX3 in the Developing Embryonic Mouse Brain and Postnatal Testes

Abstract

SOX3 is a transcription factor found within neural progenitor cells (NPC) of the developing and adult vertebrate central nervous system. SOX3 is also found in other tissues, most notably the spermatogonial progenitor/stem cell populations in the testes. Normal brain development in both humans and mice, and sperm production in mice, is reliant on the correct expression and dosage of SOX3. The function of SOX3 has been explored through a number of different cell and mouse model based techniques, however, the mechanisms through which SOX3 acts remain largely unknown. This thesis explores the genome wide DNA binding profile of SOX3 in both NPCs and postnatal testes, two very different sources of SOX3 expressing cells. We identified 8064 binding sites within NPCs derived from cultured mouse embryonic stem cells, linking SOX3 to a number of different neural development pathways. Additionally, we identified 778 SOX3 binding sites within postnatal day 7 mouse testes, linking SOX3 to the control of histones and histone variants, most of which was also true for NPCs. We utilised our Sox3 null mouse model and a number of different marker genes of spermatogenesis to identify that SOX3 is found within the committed progenitor fraction of the undifferentiated spermatogonial pool. We identified that SOX3 is required for the transition from a GFRα1+ state to a NGN3+ committed progenitor state, and in the absence of SOX3 GFRα1+ cells accumulate and spermatogonia fail to differentiate, leading to empty testes with no mature sperm. We provide further evidence that Ngn3 is a direct target of SOX3 in both NPCs and the testes albeit thought different regulatory regions. We have generated two invaluable genome wide ChIP-seq datasets that will deepen our understanding of mechanisms by which SOX3 controls context-specific differentiation. Taken together, the data presented in this thesis expand our knowledge of the genomic regions bound by SOX3 and its role in neurogenesis and spermatogenesis.