DRP1 down-regulation causes developmental defects in ovarioles and model for mitochondria’s role in cell fate determination. (A) Down-regulating DRP1 inhibits stalk cell differentiation. Left image shows the wild-type (WT) ovariole. UbiGFP labels wild-type follicle cells, and Hoechst labels DNA. Stalk cells are indicated by arrowheads. Middle image shows ovarioles with drp1^KG clones (lacking UbiGFP). Arrows indicate regions with no stalk cells. Right image shows presence of the mitotic marker pH3 label in drp1^KG clonal cells in regions marked by arrows. The boxed region is zoomed in the right. (B) Wild-type egg chambers (with UbiGFP) show FasIII enrichment in polar cells at each termini (arrows) of the egg chamber. Hoechst stains nuclei. (C) Z sectioning through mitotic egg chambers immunostained for FasIII. Sections are arranged in a series, in which numbers represent optical sections from top to bottom. Wild-type chamber (with UbiGFP) has two FasIII-enriched polar cells (arrows in sections 1 and 9). Chamber (asterisks) primarily encapsulated by drp1^KG clonal follicle cells (no UbiGFP) with only one polar cell pair (open arrow in section 4) and this wild-type FasIII-positive polar cell pair expresses UbiGFP and thus appears yellow. Hoechst stains the nuclei. (D, left) Oocyte nucleus (arrows) after normal migration to the anterior region of oocyte chamber in an S8 wild-type egg chamber. (right) Oocyte nucleus (arrows) in an S8 egg chamber containing drp1^KG PFC clones (UbiGFP negative) fails to migrate to anterior. Hoechst labels all nuclei, including that of oocyte. Bottom images show magnification of white boxes. White lines define the clone boundary. (E) Model for role of mitochondrial dynamics in determining cell fate in mitotic and postmitotic stages of follicle cell development. Bars, 10 µm.