Interactions between early germ cells and inner germarial sheath cells in Drosphila ovary

Abstract

Aim: the objective is to investigate interactions between early germ cells and inner germarial sheath cells (IGS) in Drosophila ovary. Results: in the first part, it has been shown that: 1) Stet in early germ cells cleave membrane-tethered EGFR ligand precursors to produce mature active ligands; 2) then the active ligands associate with EGFR to activate EGFR-MAPK signaling in IGS cells; 3) the activated EGFR-MAPK signaling represses Dally expression in IGS cells to restrict Dpp (BMP2/4 homologue) transportation/stability in IGS cells. In the second part, it is found that Med20 is required for pre-CB (cystoblast) or CB differentiation from a RNA interference screen. Med20 has interaction with Bam, not Dpp. And gene expression profiling of IGS cells demonstrates that Med20 affects various genes expression, including hh and dos. Conclusions: the experimental results indicate that EGFR-MAPK signaling play a pivotal role in restricting the GSC (germline stem cell) niche activity through repressing Dally expression, thus to promote CB to undergo differentiation. Furthermore, GSCs contribute to the GSC niche activity. In the other aspect, IGS cells are very important for the pre-CB or CB differentiation and these cells have a specific expression profiling of genes.