Analyses of novel regulators of Drosophila melanogaster spermatogenesis

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the La Trobe Institute of Molecular Science, College of Science, Health, and Engineering, La Trobe University, Bundoora.

Adult stem cells play an essential role in the development and maintenance of tissues throughout the lifetime of an organism. Molecular signals from the stem cell microenvironment (or niche) regulate a diversity of cell behaviours, acting to prohibit excess tissue growth and to maintain tissue homeostasis. Model systems containing stem cell niches, like the Drosophila melanogaster testis, have been instrumental in studying the genetic factors regulating stem cell self-renewal, differentiation, and proliferation, all of which are commonly disrupted in tumourigenesis. Utilising the developing Drosophila testis, a forward genetic screen was conducted to identify novel regulators of spermatogenesis and, potentially, stem cell behaviour. A number of 2nd chromosome alleles were identified, characterised, and their genetic lesions isolated. Additionally, characterisations of a previously identified 3rd chromosome allele – jam packed (jam) – were conducted, and it was identified to be an allele of a poorly understood gene: Strip. Strip encodes a highly conserved protein of as yet undetermined function, and has been implicated as having roles in a wide range of biological processes in a number of species. It is also thought to be a central component of the Striatin-interacting phosphatase and kinase (STRIPAK) complex, a newly discovered and diversely functioning protein complex. This thesis demonstrates that Strip acts within the somatic lineage of the developing Drosophila testis to autonomously regulate both morphology and differentiation, while non-autonomously influencing the proliferation and differentiation of the germline lineage. Results from this study suggest Strip acts with another STRIPAK component, Cka, and that together these molecules negatively regulate the Jun-N-terminal Kinase (JNK) signalling pathway, a previously unstudied signalling pathway in Drosophila spermatogenesis. Additionally, we demonstrated that Strip genetically interacts with Rac1, but not with components of the canonical EGFR signalling pathway during spermatogenesis. Our data indicate that by regulating JNK signalling, Strip effects proper somatic cell enclosure of the germline lineage, and hence proper spermatogenesis.