Molecular chaperone Tetratricopeptide repeat protein 2 (Tpr2) is essential for germline stem cell self-renewal and timely cyst divisions in Drosophila melanogaster oogenesis

Abstract

Steroid hormones influence cell proliferation and cell fate in developing and injured tissues. Although steroid hormone signaling has been well-studied, the precise mechanisms by which cells specifically receive steroid hormones remains largely uncharacterized. In Drosophila and many other insects, the primary steroid hormone is ecdysone, which is necessary for reproduction. Ecdysone effects have been well studied in the ovary; for example, ecdysone signaling through the Ecdysone Receptor promotes germ cell proliferation, differentiation, and survival. It is unclear, however, how Ecdysone Receptor expression or signaling is regulated in germ cells. We previously identified the molecular chaperone encoded by Tetratricopeptide repeat protein 2 (Tpr2) in a reverse genetic screen as a possible connection between ecdysone signaling and germline stem cell self-renewal. The human homolog of Tpr2, DNAJC7, can form complexes with Hsp90 and Hsp70 in vitro. Tpr2 is thought to function as a recycling cochaperone, aiding protein folding and dimerization of the glucocorticoid and progesterone receptors. Ecdysone signaling is necessary for Drosophila germline stem cell function and cyst divisions. We therefore hypothesized that Tpr2 may promote ecdysone signaling in early germ cells. As an initial test of this hypothesis, we used CRISPR mutagenesis, genetic mosaics, and germline-enhanced RNAi techniques to investigate whether Tpr2 is necessary for germ cell mitotic divisions. In the absence of Tpr2, germline stem cell self-renewal is abrogated, suggesting that Tpr2 is autonomously necessary for germline stem cell activity. Further, germ cell mitotic divisions are delayed in Tpr2 mutants, leading to fewer cysts per germarium. Our preliminary data suggest that Tpr2 mutant germ cells are slow to complete S phase, indicative of an overall slower cell cycle. Taken together, our data suggests that, like Ecdysone Receptor, Tpr2 is essential for cell cycle control in germ cells. Our studies help elucidate the molecular mechanisms by which steroid hormones promote cell division.