ß-importin Tnpo-SR promotes germline stem cell maintenance and oocyte differentiation in female Drosophila.

Germ cell development requires interplay between factors that balance cell fate and division. Early in their development, germ cells in many organisms divide mitotically with incomplete cytokinesis. Key regulatory events then lead to the specification of mature gametes, marked by the switch to a meiotic cell cycle program. Though the regulation of germ cell proliferation and meiosis are well understood, how these events are coordinated during development remains incompletely described. Originally characterized in their role as nucleo-cytoplasmic shuttling proteins, ß-importins exhibit diverse functions during male and female gametogenesis. Here, we describe novel, distinct roles for the ß-importin, Transportin-Serine/Arginine rich (Tnpo-SR), as a regulator of the mitosis to meiosis transition in the Drosophila ovary. We find that Tnpo-SR is necessary for germline stem cell (GSC) establishment and self-renewal, likely by controlling the response of GSCs to bone morphogenetic proteins. Depletion of Tnpo-SR results in germ cell counting defects and loss of oocyte identity. We show that in the absence of Tnpo-SR, proteins typically suppressed in germ cells when they exit mitosis fail to be down-regulated, and oocyte-specific factors fail to accumulate. Together, these findings provide new insight into the balance between germ cell division and differentiation and identify novel roles for ß-importins in germ cell development.

Sexual dimorphism in the dorsal root ganglia of neonatal mice identified by protein expression profiling with single-cell mass cytometry.

Development of neuronal and glial populations in the dorsal root ganglia (DRG) is required for detection of touch, body position, temperature, and noxious stimuli. While female-male differences in somatosensory perception have been previously reported, no study has examined global sex differences in the abundance of DRG cell types, and the developmental origin of these differences has not been characterized. To investigate whether sex-specific differences in neuronal and glial cell types arise in the DRG during development, we performed single-cell mass cytometry analysis on sex-separated DRGs from 4 separate litter replicates of postnatal day 0 (P0) C57/BL6 mouse pups. In this analysis, we observed that females had a higher abundance of total neurons (p = 0.0266), as well as an increased abundance of TrkB+ (p = 0.031) and TrkC+ (p = 0.04) neurons for mechanoreception and proprioception, while males had a higher abundance of TrkA+ (p = 0.025) neurons for thermoreception and nociception. Pseudotime comparison of the female and male datasets indicates that male neurons are more mature and differentiated than female neurons at P0. These findings warrant further studies to determine whether these differences are maintained across development, and their impact on somatosensory perception.

Orphan nuclear receptor ftz-f1 (NR5A3) promotes egg chamber survival in the Drosophila ovary.

Gamete production in mammals and insects is controlled by cell signaling pathways that facilitate communication between germ cells and somatic cells. Nuclear receptor signaling is a key mediator of many aspects of reproduction, including gametogenesis. For example, the NR5A subfamily of nuclear receptors is essential for gonad development and sex steroid production in mammals. Despite the original identification of the NR5A subfamily in the model insect Drosophila melanogaster, it has been unclear whether Drosophila NR5A receptors directly control oocyte production. Ftz-f1 is expressed throughout the ovary, including in germline stem cells, germline cysts, and several populations of somatic cells. We show that ftz-f1 is required in follicle cells prior to stage 10 to promote egg chamber survival at the mid-oogenesis checkpoint. Our data suggest that egg chamber death in the absence of ftz-f1 is due, at least in part, to failure of follicle cells to exit the mitotic cell cycle or failure to accumulate oocyte-specific factors in the germline. Taken together, these results show that, as in mammals, the NR5A subfamily promotes maximal reproductive output in Drosophila. Our data underscore the importance of nuclear receptors in the control of reproduction and highlight the utility of Drosophila oogenesis as a key model for unraveling the complexity of nuclear receptor signaling in gametogenesis.

Novel cis-regulatory regions in ecdysone responsive genes are sufficient to promote gene expression in Drosophila ovarian cells.

The insect steroid hormone ecdysone is a key regulator of oogenesis in Drosophila melanogaster and many other species. Despite the diversity of cellular functions of ecdysone in oogenesis, the molecular regulation of most ecdysone-responsive genes in ovarian cells remains largely unexplored. We performed a functional screen using the UAS/Gal4 system to identify non-coding cis-regulatory elements within well-characterized ecdysone-response genes capable of driving transcription of an indelible reporter in ovarian cells. Using two publicly available transgenic collections (the FlyLight and Vienna Tiles resources), we tested 62 Gal4 drivers corresponding to ecdysone-response genes EcR, usp, E75, br, ftz-f1 and Hr3. We observed 31 lines that were sufficient to drive a UAS-lacZ reporter in discrete cell populations in the ovary. Reporter expression was reproducibly observed in both somatic and germ cells at distinct stages of oogenesis, including those previously characterized as critical points of ecdysone regulation. Our studies identified several useful new reagents, adding to the UAS/Gal4 toolkit available for genetic analysis of oogenesis in Drosophila. Further, our study provides novel insight into the molecular regulation of ecdysone signaling in oogenesis.