Loss- and gain-of-function analyses of the role of MAP kinase signalling in testis determination

Thesis

Sexual differentiation is the process by which an organism develops as either male or female. In mammals, this process is governed chromosomally, principally by the presence or absence of the Y chromosome. In the mouse, sex determination occurs at 11.5 days post coitum (dpc), when expression of Sry in the XY gonad kick-starts testis determination. SRY drives the subsequent expression of genes that both promote testis differentiation and inhibit ovarian differentiation, leading to specification of the testis. In cases where sex determination is disrupted, disorders of sexual development (DSD) can occur. Many genes have been described that are required for testis determination. However, we still know relatively little about how Sry itself is regulated.

MAP kinase (MAPK) signalling is involved in testis determination in mice and humans. MAP3K4 is required for testis determination in the mouse: loss of MAP3K4 is associated with male-to-female sex reversal in embryos and insufficient expression of Sry at 11.5 dpc. Likewise, loss of function of a protein known to interact with MAP3K4, GADD45γ, also leads to sex reversal. In humans, mutations in the gene encoding the related kinase, MAP3K1, have been identified as a key cause of DSD. Thus, MAPK signalling appears to play a key role in testis determination both in humans and mice.

This thesis describes experiments designed to further elucidate the role of MAPK-related signalling in testis determination. Firstly, an attempt was made to generate mice bearing a human sex-reversing mutation in Map3k1, however this was not successful. Additionally, RNA-seq was employed to investigate transcriptional targets of GADD45γ. Finally, the role of MAP3K4 as a dose-dependent modifier of sensitivity to sex reversal in mice is described, utilising a Map3k4 transgene to rescue sex reversal in B6 mice harbouring a Y chromosome from the Mus poschiavinus strain. These mice undergo sex reversal in the absence of the Map3k4 transgene, and also exhibit delayed Sry expression. By utilising this genetic tool, this thesis investigates the mechanism of sex reversal in these mice, with particular focus on the role pf Map3k4 in Sry expression.

Authors: Pope, M

• DOI: 10.5287/ora-kzggqeeo6
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Keywords: sex determination; MAPK; testis; GADD45; Genetics
• Subjects: Genetics; Sex determination, Genetic