Date Thesis Awarded

5-2014

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Shanta D. Hinton

Committee Member

Mark Forsyth

Committee Member

Douglas Young

Abstract

Stem cells are vital for organogenesis, tissue regeneration, and tissue homeostasis. These asymmetrically dividing cells provide the functional cell types necessary for organogenesis while maintaining a stem cell population that continuously replaces damaged and dying cells. Despite the fundamental importance of stem cells to living systems, the mechanisms regulating stem cell development are not well understood. One of the most thoroughly studied systems for examining stem cell behavior is the stem cell niche in the adult Drosophila testis. This niche is composed of two populations of stem cells: the sperm-producing germline stem cells (GSCs) and the somatic cyst stem cells (CySCs). Both of these populations are anchored around a cluster of non-mitotic somatic cells found at the testis apex, called the hub. Within this stem cell niche, the Bone Morphogenetic Protein (BMP) pathway has been shown to regulate GSC maintenance in the adult organism. In this thesis, we examine the role of BMP signaling during the dynamic process of development. Specifically, we characterize the pattern of BMP activation in the testis throughout development, determine the role of BMP signaling in the maintenance of GSCs in larval testes, assess the role of BMP signaling on cyst cell function, and evaluate interactions between the BMP pathway and Jak-STAT, another pathway known to regulate CySC behavior. We find that BMP signaling expresses a dynamic pattern of activation in developing primordial germ cells (PGCs) during embryogenesis, and that BMP activation becomes restricted to GSCs and germ cells in the testis anterior after hub formation. Additionally, we find that BMP signaling is both necessary and sufficient for the maintenance of undifferentiated GSCs in the early larval testis and that in the soma it is required for proper spermatogonial differentiation. Finally, we show that soma-specific Jak-STAT hyperactivation results in expanded expression of BMP signaling, indicating interactions between the CySCs and the GSCs using the BMP pathway. Thus, our results show that BMP signaling from the CySCs promotes GSC maintenance and demonstrates the importance of soma-germline communication in spermatogonial differentiation. Furthermore, the research presented in this thesis suggests other possible roles for BMP signaling in testis development, including a possible function in GSC establishment, as well as the existence of a second pathway that helps promote GSC maintenance during late stages of testis development.

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Available for download on Tuesday, May 07, 2019

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