Genetic dissection of a stem cell niche: The case of the Drosophila ovary

Abstract

In this work, we demonstrate a powerful new tool for the manipulation of the stromal component of a wellestablished Drosophila stem cell niche. We have generated a bric-a-brac 1 (bab1)-Gal4 line that drives UAS expression in many somatic ovary cell types from early larval stages. Using this Gal4 line, we could effectively induce FLP/FRT-mediated recombination in the stromal cells of the ovarian germline stem cell niche. Mutant clones were observed in the developing ovary of larvae and pupae, including in somatic cell types that do not divide in the adult, such as the cap cells and the terminal filament cells. Exploiting the ability of bab1-Gal4 to generate large clones, we demonstrate that bab1-Gal4 is an effective tool for analyzing stem cell niche morphogenesis and cyst formation in the germarium. We have identified a novel requirement for engrailed in the correct organization of the terminal filaments. We also demonstrate an involvement for integrins in cyst formation and follicle cell encapsulation. Finally using bab1-Gal4 in conjunction with the Gal80 system, we show that while ectopic dpp expression from stromal cells is sufficient to induce hyperplastic stem cell growth, neither activation nor inactivation of the BMP pathway within stromal cells affects germline stem cell maintenance.

Novel Tools for Genetic Manipulation of Follicle Stem Cells in the Drosophila Ovary Reveal an Integrin-Dependent Transition from Quiescence to Proliferation

“…In terminal filament and cap cells, for example, weak expression of growth factors may be achieved using boi-Gal4 or sgg-Gal4 without having dramatic effects on the development of the fly (Figure 2). bab-Gal4 remains the most robust driver for terminal filament and cap cells, with many examples of its successful use for reducing gene expressing with RNAi (Bolívar et al 2006;Hartman et al 2010Hartman et al , 2013Sahai-Hernandez and Nystul 2013;Xin et al 2013). All the Gal4 lines we identified that promoted expression in IGS cells also exhibited expression in other cell types, including cap cells, FSCs, and/or pre-follicle cells.…”

The cytolinker Pigs is a direct target and a negative regulator of Notch signalling

“…Expression of this construct under the control of the engrailed or bab1 promoter (Bolivar et al, 2006) led to encapsulation defects and abnormal stalk morphology (Fig. 2K-M).…”

The Development of Germline Stem Cells in Drosophila

“…Cap cell differentiation occurs in early pupae as TF formation is completed. The niche develops by cell rearrangement and cell recruitment, so that an individual niche is polyclonal in origin, technically limiting the ability to perform genetic loss-of-function studies in the niche (68,69). Advances in available genetic tools, such as the recent development of a method to target clone formation to the somatic gonadal cells (69), hold promise to expand the genetic analysis of niche morphogenesis and GSC maintenance.…”