Doctor of Philosophy (PhD)
Changes to societal norms, such as the educational, marital, and child-bearing expectations have coincided with significant increases in infertility worldwide. Surprisingly, male infertility is responsible for approximately half of all infertility cases worldwide. Thus, a better understanding of sperm development, and how it is affected by age, may permit the design and application of therapeutics to treat various cases male infertility. Here, I have found that lysosomes acidify as germ cells enter the spermatocyte stage. Once active, lysosomes turn over E-cadherin, and likely other proteins, to support plasma membrane stability. Notably, aging negatively impacts lysosome acidification, which can be reversed upon pharmacological inhibition of Target of Rapamycin (TOR) signaling. The natural aging process yielded similar defects in the germline as those observed upon inhibition of lysosome acidification, such as germ-cell multinucleation. Intriguingly, I found that a positive regulator of lysosome acidification, AMPK, is negatively affected by age. Similarly, an AMPK target, Mitf, the master regulator of lysosome biogenesis, is less active in the aged male germline. The deregulation of this signaling axis hints at a potential mechanism by which lysosome acidity is diminished in the aging male germline. Around the same time as lysosomes acidify, I found that Valosin-containing protein (VCP) translocates from the cytosol in mitotic spermatogonia to the nucleus in meiotic spermatocytes. Significantly, nuclear entry of VCP depends upon testis-specific TBP-associated factors (tTAFs), and, similar to tTAFs, VCP is required for spermatocyte differentiation. Intriguingly, VCP controls gene expression and spermatocyte differentiation downstream of tTAFs by downregulating mono-ubiqutinated H2A (H2Aub), a repressive histone modification. Using a novel Gal4 driver, I was able to identify additional roles for VCP in later stages of spermatogenesis; VCP supports spermatid chromatin condensation and spermatid individualization.
Butsch, Tyler James, "Switch-like Behavior of Lysosomes and VCP Supports Spermatocyte Health and Development in Drosophila" (2023). LSU Doctoral Dissertations. 6075.
Bohnert, K. Adam
Available for download on Saturday, March 30, 2024