The Bric-à-Brac BTB/POZ transcription factors are necessary in niche cells for germline stem cells establishment and homeostasis through control of BMP/DPP signaling in the Drosophila melanogaster ovary

Niche formation and function in developing tissue: studies from the Drosophila ovary

Adult stem cells have a unique ability to self-renew and to generate differentiated daughter cells that are required in the body tissues. The identity of adult stem cells is maintained by extrinsic signals from other cell types, known as niche cells. Thus, the niche is required for appropriate tissue homeostasis. Niche is formed and recruits stem cells during tissue development; therefore, it is essential to establish niche cells and stem cells in proper numbers during development. A small niche may recruit too few stem cells and cause tissue degeneration, while a large niche may maintain too many stem cells and lead to tumorigenesis. Given that vertebrate tissues are not suitable for large-scale forward genetics studies, the Drosophila ovary stands out as an excellent model for studying how multiple niche cell types and germ cells (GCs) are coordinately regulated in vivo. Recent studies are beginning to reveal how various signaling molecules regulate niche formation and how niche cells non-autonomously influence GC number. In this review, we summarize the ovarian niche structure, the key signaling pathways for niche formation, and how niche cells generate extrinsic factors to control GC proliferation during ovarian development. Video abstract.

A dual role of lola in Drosophila ovary development: regulating stem cell niche establishment and repressing apoptosis

In Drosophila ovary, niche is composed of somatic cells, including terminal filament cells (TFCs), cap cells (CCs) and escort cells (ECs), which provide extrinsic signals to maintain stem cell renewal or initiate cell differentiation. Niche establishment begins in larval stages when terminal filaments (TFs) are formed, but the underlying mechanism for the development of TFs remains largely unknown. Here we report that transcription factor longitudinals lacking (Lola) is essential for ovary morphogenesis. We showed that Lola protein was expressed abundantly in TFCs and CCs, although also in other cells, and lola was required for the establishment of niche during larval stage. Importantly, we found that knockdown expression of lola induced apoptosis in adult ovary, and that lola affected adult ovary morphogenesis by suppressing expression of Regulator of cullins 1b (Roc1b), an apoptosis-related gene that regulates caspase activation during spermatogenesis. These findings significantly expand our understanding of the mechanisms controlling niche establishment and adult oogenesis in Drosophila.

Distinct gene expression dynamics in germ line and somatic tissue during ovariole morphogenesis in Drosophila melanogaster

The survival and evolution of a species is a function of the number of offspring it can produce. In insects, the number of eggs that an ovary can produce is a major determinant of reproductive capacity. Insect ovaries are made up of tubular egg-producing subunits called ovarioles, whose number largely determines the number of eggs that can be potentially laid. Ovariole number in Drosophila is directly determined by the number of cellular structures called terminal filaments, which are stacks of cells that assemble in the larval ovary. Elucidating the developmental and regulatory mechanisms of terminal filament formation is thus key to understanding the regulation of insect reproduction through ovariole number regulation. We systematically measured mRNA expression of all cells in the larval ovary at the beginning, middle, and end of terminal filament formation. We also separated somatic and germ line cells during these stages and assessed their tissue-specific gene expression during larval ovary development. We found that the number of differentially expressed somatic genes is highest during the late stages of terminal filament formation and includes many signaling pathways that govern ovary development. We also show that germ line tissue, in contrast, shows greater differential expression during early stages of terminal filament formation, and highly expressed germ line genes at these stages largely control cell division and DNA repair. We provide a tissue-specific and temporal transcriptomic dataset of gene expression in the developing larval ovary as a resource to study insect reproduction.