Date Thesis Awarded

5-2022

Access Type

Honors Thesis -- Open Access

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Matthew Wawersik

Committee Members

Dana Lashley

Jennifer Bestman

Lizabeth Allison

Abstract

Stem cells are crucial for both organogenesis and tissue homeostasis. They asymmetrically divide to promote proliferation and differentiation during development, as well as replenish damaged and aging cells in adult tissues. Investigation of stem cell behavior has already yielded tremendous advances in medicine including development of strategies to treat several types of cancer. Stem cells, however, are not yet fully understood and further work promises to advance medical treatments. To date, one of the most well characterized models for stem cell behavior is the Drosophila testes stem cell niche. This niche is composed of two stem cell populations: germline stem cells (GSCs), which develop to produce sperm, and cyst stem cells (CySCs), which encase and provide instructions for GSCs division and differentiation. These two populations are found attached to a quiescent cell population in the apex of the testis, the hub cells. These three cell types are known to keep in constant communication to modulate gene activation and maintain a healthy balance of GSCs division and differentiation. Therefore, studying this genetic modulation is a key step to holistic understanding of stem cell behavior. Our lab found a novel protein, Childless Gambino (Chigno), to be expressed in the stem cell niche of adult ovaries and testes (ref Natalie’s thesis). Furthermore, RNAi expression to disrupt Chigno function in the adult somatic gonad was found to cause partial infertility in flies (Claybrook M.A. thesis 2019). In this thesis, Chigno expression is characterized through development with an emphasis in the gonads. Chigno function is further explored through disruption in all cells within the developing organism as well as specifically in the somatic gonad. When studying reproductive tissues, both testes and ovaries were investigated for Chigno function. We found that Chigno expression starts in subnuclear punctae in all three germ layers at the beginning of gastrulation coinciding with zygotic gene activation (ZGA). As development progresses, noteworthy tissues that express Chigno are the midgut, muscle, tracheal system, and gonads. Within the gonads, Chigno is found to be expressed in germ cells and somatic cells, with localization in the germline broader than it is in somatic cells. When Chigno function is disrupted in all developing development, late embryos stall when hatching to L1 larvae. When chigno RNAi is expressed in the somatic gonad during development, both males and females are found to be irreversibly sterile. Furthermore, morphological analysis of these somatic chigno RNAi testes and ovaries reveals severe underdevelopment. Testes show undifferentiated germ cell and hub expansion, while ovaries exhibit germline proliferation, fusome degeneration, and signs of somatic cells failing to differentiate. This thesis provides solid ground for future mechanistic analysis of Chigno’s role during development.

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Available for download on Thursday, May 13, 2027

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