Understanding the function of the transcriptional activator ZFY in relation to its structure and evolution

The Y chromosome is a small, gene-poor chromosome that is enriched with repetitive sequences. This is due to its inability to undergo recombination, which leads to genetic degeneration over evolutionary time. Consequently, it is sometimes regarded as a “functional wasteland”. The genes that persist on the Y chromosome are essential for sex determination and male germ cell development. Among these, the transcription factor ZFY is one of very few genes consistently present on the Y chromosome in almost all eutherian species, indicating that it must have essential functions in men. A further distinctive feature of ZFY is the presence of two distinct developmentally regulated splice variants; a ubiquitous full-length major variant and a testis-specific minor short variant. This thesis seeks to understand the evolution, structure and function of ZFY, building on recent theoretical advances in understanding the mechanisms of transcription factor activity, and on up-to-date transcriptomic and proteomic experimental techniques. This thesis comprises four results chapters that collectively probe different aspects of ZFY structure and function. First, a phylogenetic analysis defines conserved versus rapidly evolving regions of ZFY and relates this to newly predicted functional motifs within the acidic domain. Secondly, cross-species examination of ZFY splicing data reveals that the testis-specific splicing pattern predates its recruitment to the Y chromosome, and potentially implicates RBMY as a potential splicing factor involved. Thirdly, RNA-Seq analysis highlights the core downstream pathways regulated by each splice isoform of ZFY, and finally pull-down proteomics identifies a range of potential interacting partners. Overall, the results identify a potential novel feedback loop regulating ZFY splicing during testis development and suggest several key pathways that ZFY may regulate including WNT signalling, ErbB signalling and extracellular matrix remodelling. Whilst an earlier observation that the short ZFY form is mis-expressed in some cancers was replicated, a wider role for ZFY as a cancer-testis gene was generally not supported.