A Component of the Proteasome Regulatory Subunit, Rpn3, Modulates Border Cell Migration in Drosophila Oogenesis

Karmakar, Susnata (2022) A Component of the Proteasome Regulatory Subunit, Rpn3, Modulates Border Cell Migration in Drosophila Oogenesis. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Susnata Karmakar (14RS034)) 14RS034.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

Cellular movement is an important process aiding all of metazoan development. It is a crucial process that is involved in several biological processes, including tissue formation, organogenesis, wound healing, immune response, and also cancer metastasis. Though proteasomes have been implicated in regulating cellular movement, the underlying molecular mechanism is far from clear. The Proteasomes are a multisubunit catalytic cellular machinery that can selectively eliminate protein molecules targeted for degradation. We have employed the border cell (BC) migration during Drosophila oogenesis as a model to understand how proteasomes regulate cellular movement. In the first half of the thesis (Chapter 3), I have downregulated the protein degradation processes during oogenesis to see if BC movement gets affected. Impaired migration upon treatments inspired me to screen for candidate genes that lead to the identification of Rpn3. Having established that it was indeed the downregulation of the Rpn3 transcripts that resulted in the inefficient migration, I went on to generate genetic knock-out mutants in Drosophila. In chapter 4, I have characterized the biological processes that correlate with the inefficient migration to narrow down on the signaling pathways that could be affected. My analysis revealed that the detachment of the BC cluster from the neighbouring epithelium seems to have been impacted upon Rpn3 knockdown, apart from subtle mislocalization of polarity marker proteins. Subsequently (in Chapter 5), I provide evidence to support that the inability to degrade a Protein Tyrosine Kinase molecule, Src, results in the observed defects upon proteasomal downregulation. Overexpression of a constitutively active form of the kinase phenocopied the Rpn3 downregulation phenotype, and genetic manipulations to bring down the kinase activity were able to rescue the observed defects in BC detachment. In short, this work demonstrates the requirement of the proteasomal degradation of an Src homolog for successful detachment of BCs during Drosophila oogenesis. The dysregulation of the kinase activity of Src being implicated as a transforming factor in multiple tumors and the use of proteasome inhibitors in the treatment of several tumor malignancies help to bring into perspective the importance of these findings.

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