Characterizing the function of zinc-finger transcription factor crooked legs in Drosophila oogenesis

Abstract

In the Drosophila ovary, a network of intracellular and extracellular factors regulate the transition from germ cell to viable oocyte. Cross-talk between germline and somatic cells must be maintained throughout oogenesis to ensure cells move and differentiate in tandem to support the growing oocyte. One process that is facilitated by germline-soma communication is germline cyst encapsulation, an essential somatic cell behavior during which follicle cells migrate to surround germline cysts. Cyst encapsulation is required to establish proper egg chamber architecture and ultimately ensures the cellular environment can sustain a viable egg. Among the signals driving these cellular changes, the steroid hormone ecdysone is required in both the germline and soma to support normal oocyte development. Despite its established role in oogenesis, the transcriptional targets of ecdysone, and their putative roles in ovarian cell function, remain largely uncharacterized. Our previous studies using single cell RNA-sequencing revealed a zinc-finger transcription factor, crooked legs (crol), as a prospective ecdysone transcriptional target in the ovary. Previous studies characterized crol as an orchestrator of metamorphosis and a necessary coordinator of imaginal disc development. However, its role in oogenesis remains unclear. Here, we show crol is endogenously expressed in both germline and somatic cells of the ovary. To investigate a somatic role for crol, we depleted its expression in various follicle cell populations using RNAi-based methods. We find that crol deficiency in early follicle cells disrupts the movement and organization of germline cysts, and follicle cells fail to encapsulate cysts. When crol is depleted in both undifferentiated and differentiated follicle cells, these defects escalate, resulting in the formation of large compound egg chambers containing an excess of nurse cells, consistent with failed or incomplete encapsulation. To further define a requirement for crol in the soma, we generated genetic mosaics to assess how crol-null follicle cell clones impact oogenesis. Germaria containing crol-null somatic clones also exhibited significant cyst encapsulation defects. These results suggest a novel role for a previously uncharacterized transcription factor in maintaining proper encapsulation and progression of developing germ cells through autonomous somatic cell signaling, and a function as an ecdysone-induced transcriptional regulator throughout oogenesis.