Hellberg, J. E. E. U. | bioRxiv Science

bioRxiv2021

Rbf/E2F1 control growth and endoreplication via steroid-independent Ecdysone Receptor signalling in Drosophila prostate-like secondary cells

Dysregulation of cell cycle components results in the development and progression of several cancer types. Unusually, loss of the tumour suppressor gene, Retinoblastoma (Rb), and consequent activation of transcription factor E2F1 have been linked to late-stage tumour progression in prostate cancer, rather than early-stage events. This change is associated with an androgen-independent form of cancer, castration-resistant prostate cancer (CRPC), which frequently still requires androgen receptor (AR) signalling. We have previously shown that binucleate secondary cells (SCs) of the Drosophila melanogaster male accessory gland (AG) share several functional and signalling similarities with human prostate epithelial cells. Upon mating, SC growth regulation switches from a steroid-dependent to a steroid-independent form of Ecdysone Receptor (EcR) control that induces genome endoreplication. Here, we demonstrate that the Drosophila Rb homologue, Rbf, and E2F1, as well as cell cycle regulators, Cyclin D (CycD) and Cyclin E (CycE), are key mediators of SC growth and endoreplication both in virgin and mated males. Importantly, we show that the CycD/Rbf/E2F1 axis requires the EcR, but not ecdysone, to trigger CycE-dependent endoreplication and associated growth in SCs after mating, mirroring changes in CRPC. We also demonstrate that excess Rbf activity reversibly suppresses binucleation in adult SCs. Overall, our work reveals mechanistic parallels between the physiological switch to hormone-independent EcR signalling in SCs, and the pathological switch seen in CRPC, and suggests that the latter may represent the dysregulation of a currently unidentified physiological process, which permits AR signalling when androgen levels are low.

cell biology↗

bioRxiv2020

Drosophila Sex Peptide Controls the Assembly of Lipid Microcarriers in Seminal Fluid

Seminal fluid plays an essential role in promoting male reproductive success and modulating female physiology and behaviour. In the fruit fly, Drosophila melanogaster, Sex Peptide (SP) is the best-characterised protein mediator of these effects. It is secreted from the paired male accessory glands (AGs), which, like the mammalian prostate and seminal vesicles, generate most of the seminal fluid contents. After mating, SP binds to spermatozoa and is retained in the female sperm storage organs. It is gradually released by proteolytic cleavage and induces several long-term post-mating responses including ovulation, elevated feeding and reduced receptivity to remating, primarily signalling through the SP receptor (SPR). Here, we demonstrate a previously unsuspected SPR-independent function for SP. We show that, in the AG lumen, SP and secreted proteins with membrane-binding anchors are carried on abundant, large neutral lipid-containing microcarriers, also found in other SP-expressing Drosophila species. These microcarriers are transferred to females during mating, where they rapidly disassemble. Remarkably, SP is a key assembly factor for microcarriers and is also required for the female disassembly process to occur normally. Males expressing non-functional SP mutant proteins that affect SPs binding to and release from sperm in females also do not produce normal microcarriers, suggesting that this male-specific defect contributes to the resulting widespread defects in ejaculate function. Our data therefore reveal a novel role for SP in formation of seminal macromolecular assemblies, which may explain the presence of SP in Drosophila species, which lack the signalling functions seen in D. melanogaster. Significance StatementSeminal fluid plays a critical role in reprogramming female physiology and behaviour to promote male reproductive success. We show in the fruit fly that specific seminal proteins, including the archetypal female-reprogramming molecule Sex Peptide, are stored in male seminal secretions in association with large neutral lipid-containing microcarriers, which rapidly disperse in females. Related structures are also observed in other Sex Peptide-expressing Drosophila species. Males lacking Sex Peptide have structurally defective microcarriers, leading to abnormal cargo loading and transfer to females. Our data reveal that this key signalling molecule in Drosophila seminal fluid is also a microcarrier assembly factor that controls transfer of other seminal factors, and that this may be a more evolutionarily ancient role of this protein.

cell biology↗