Understanding border cell fate specification and micropyle formation during Drosophila oogenesis

Saha, Banhisikha (2019) Understanding border cell fate specification and micropyle formation during Drosophila oogenesis. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Banhisikha Saha (13RS008)) 13RS008.pdf - Submitted Version Restricted to Repository staff only Download (7MB)

Abstract

Inter-cellular communication is one of the fundamental processes that co-ordinate the development of a multi-cellular organism and helps them to acquire different cell fate required to perform specific functions. One such example of intercellular communication is germline-somatic communication, which is critical for the development of successful gametes. Drosophila oogenesis serves to be an excellent model to study germline-somatic communication during cell fate specification as it involves the association of germline and somatic cells throughout the entire span of egg chamber maturation. Specification and migration of a small migratory group of cells called border cells during Drosophila oogenesis are indispensable for functional egg development. My work elucidates the novel role of germline-somatic communication in border cell fate specification during Drosophila oogenesis. This work elaborates the importance of cellular cytoskeleton in mediating communication with other cells that eventually leads to different cell fate specification. My work identifies a novel germline component of the Drosophila egg chamber, Cup that maintains the germline cell cytoskeleton and facilitates Notch signal activation in the adjacent somatic epithelium of the egg chamber. The Notch signaling acts antagonistically to the JAK-STAT signaling and restricts the domain of JAK-STAT activation in the anterior follicle cells. This leads to an optimum number of cells to acquire border cell fate and recruit in the cluster. My data sheds light upon the non-conventional function of Cup in regulating cellular cytoskeleton apart from its role in mRNA transport and stabilization. The most important function of the border cell cluster is to form a channel in the egg chamber membrane, which allows sperm entry during fertilization. However, the molecular mechanism underlying this event was not clear so far. The last part of my work describes how a small polar cell dramatically changes its shape to form a thin protrusion that aids in forming a hole in the egg membrane. Dissecting the molecular mechanism of this event reveals that the polar cells in the border cell cluster extend a microtubule-dependent protrusion, which is highly dynamic. This event is initiated at stage 13 of oogenesis, and moreover, this cellular shape transition is independent of border cell migration. JAK-STAT pathway is crucial for the polar cell protrusion formation with some contribution from the Wnt signaling pathway. This work encompasses the study of the molecular mechanism of two important events of development: cell fate specification and shape transition using border cell cluster as the model and explains how the border cell plays an important role in forming functional eggs that determine the fertility of in female Drosophila.

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