Genetic Analysis of a Spontaneous Mutation Disrupting Midline Localization in Drosophila Follicular Epithelium Cells

In the Drosophila ovary, the developing germline is surrounded by an epithelium of somatic follicle cells. This epithelium displays dynamic patterning by transcription factors throughout oogenesis, and these transcription factors play a crucial role in specifying cell fates within the developing egg. Previous studies have identified Midline (Mid), a T-box transcription factor, as one such regulator. Mid is expressed in the posterior region of the follicular epithelium cells in response to epidermal growth factor receptor (EGFR) signaling early in oogenesis, and its expression remains restricted to these cells during later stages. Mid is detected in the nuclei of the cells, as predicted for a transcription factor, but it is first translated in the cytoplasm of the cell before localizing to the nucleus. Mid immunofluorescent staining in wild-type follicular epithelia has also been observed to be occasionally cytoplasmic. Together this suggests potential dynamic regulation of Mid subcellular distribution; however, the underlying mechanisms remain unclear. We have identified a recessive mutation, referred to as r12m, that is associated with defective nuclear localization of Mid. In clones of follicle cells that are homozygous for r12m, Mid levels are reduced and Mid appears mislocalized from the nucleus, presenting as a hazy cytoplasmic smear rather than being clearly located within nuclei. We are conducting exploratory genetic analysis using techniques such as complementation tests, genetic mapping, and candidate gene testing to map the r12m mutation and identify the affected gene, with the goal of advancing our understanding of Mid regulation and subcellular localization.