Nutrient conditions sensed by the reproductive organ during development optimize male fecundity in Drosophila.

Nutrient conditions affect the reproductive potential and lifespan of many organisms through the insulin signaling pathway. Although this is well characterized in female oogenesis, nutrient-dependent regulation of fertility/fecundity in males is not known. Seminal fluid components synthesized in the accessory gland are required for high fecundity in Drosophila males. The accessory gland is composed of two types of binucleated cells: a main cell and a secondary cell (SC). The transcription factors Defective proventriculus (Dve) and Abdominal-B (Abd-B) are strongly expressed in adult SCs, whose functions are essential for male fecundity. We found that gene expression of both Dve and Abd-B was down-regulated under nutrient-poor conditions. In addition, nutrient conditions during the pupal stage affected the size and number of SCs. These morphological changes clearly correlated with fecundity, suggesting that SCs act as nutrient sensors. Here, we provide evidence that Dve associates nutrient conditions with optimal reproductive potential in a target of rapamycin signaling-dependent manner.

Binucleation of Accessory Gland Lobe Contributes to Effective Ejection of Seminal Fluid in Drosophila melanogaster.

The adult male accessory gland in insects is an internal reproductive organ analogous to the mammalian prostate, and secretes various components in the seminal fluid. Products of the accessory gland in the fruit fly Drosophila melanogaster are known to control reproductive behaviors in mated females, such as food uptake, oviposition rate, and rejection of re-mating with other males, all of which increase male reproductive capacity. Production of larger amounts of accessory gland products is thus thought to result in higher male reproductive success. The epithelium of the Drosophila accessory gland lobe is composed of a unique population of binucleate cells. We previously predicted, based on measurements of cell size in mono/binucleate mosaic accessory glands, that binucleation results in a higher plasticity in cell shape, enabling more effective ejection of seminal fluid. However, the actual effect of binucleation on ejection of seminal fluid or reproductive capacity remained unclear, as we were unable to generate an organ with uniformly mononucleate cells. In the present study, we generated organs in which most of the epithelial cells are mononucleate by manipulating aurora B or fizzy-related to block binucleation. Mononucleation resulted in a less elastic accessory gland lobe, which decreased ejection volume and the oviposition of mated females; these effects were particularly pronounced over the long term. These results suggest that binucleation in accessory gland epithelial cells contributes to higher plasticity in the volume of this organ, and enhances male reproductive success through enabling ejection of larger amounts of seminal fluid.

Isoform-specific functions of Mud/NuMA mediate binucleation of Drosophila male accessory gland cells.

BACKGROUND: In standard cell division, the cells undergo karyokinesis and then cytokinesis. Some cells, however, such as cardiomyocytes and hepatocytes, can produce binucleate cells by going through mitosis without cytokinesis. This cytokinesis skipping is thought to be due to the inhibition of cytokinesis machinery such as the central spindle or the contractile ring, but the mechanisms regulating it are unclear. We investigated them by characterizing the binucleation event during development of the Drosophila male accessory gland, in which all cells are binucleate. RESULTS: The accessory gland cells arrested the cell cycle at 50 hours after puparium formation (APF) and in the middle of the pupal stage stopped proliferating for 5 hours. They then restarted the cell cycle and at 55 hours APF entered the M-phase synchronously. At this stage, accessory gland cells binucleated by mitosis without cytokinesis. Binucleating cells displayed the standard karyokinesis progression but also showed unusual features such as a non-round shape, spindle orientation along the apico-basal axis, and poor assembly of the central spindle. Mud, a Drosophila homolog of NuMA, regulated the processes responsible for these three features, the classical isoform Mud(PBD) and the two newly characterized isoforms Mud(L) and Mud(S) regulated them differently: Mud(L) repressed cell rounding, Mud(PBD) and Mud(S) oriented the spindle along the apico-basal axis, and Mud(S) and Mud(L) repressed central spindle assembly. Importantly, overexpression of Mud(S) induced binucleation even in standard proliferating cells such as those in imaginal discs. CONCLUSIONS: We characterized the binucleation in the Drosophila male accessory gland and examined mechanisms that regulated unusual morphologies of binucleating cells. We demonstrated that Mud, a microtubule binding protein regulating spindle orientation, was involved in this binucleation. We suggest that atypical functions exerted by three structurally different isoforms of Mud regulate cell rounding, spindle orientation and central spindle assembly in binucleation. We also propose that Mud(S) is a key regulator triggering cytokinesis skipping in binucleation processes.

The homeodomain protein defective proventriculus is essential for male accessory gland development to enhance fecundity in Drosophila.

The Drosophila male accessory gland has functions similar to those of the mammalian prostate gland and the seminal vesicle, and secretes accessory gland proteins into the seminal fluid. Each of the two lobes of the accessory gland is composed of two types of binucleate cell: about 1,000 main cells and 40 secondary cells. A well-known accessory gland protein, sex peptide, is secreted from the main cells and induces female postmating response to increase progeny production, whereas little is known about physiological significance of the secondary cells. The homeodomain transcriptional repressor Defective proventriculus (Dve) is strongly expressed in adult secondary cells, and its mutation resulted in loss of secondary cells, mononucleation of main cells, and reduced size of the accessory gland. dve mutant males had low fecundity despite the presence of sex peptide, and failed to induce the female postmating responses of increased egg laying and reduced sexual receptivity. RNAi-mediated dve knockdown males also had low fecundity with normally binucleate main cells. We provide the first evidence that secondary cells are crucial for male fecundity, and also that Dve activity is required for survival of the secondary cells. These findings provide new insights into a mechanism of fertility/fecundity.