Fig. 2. Equal distribution of mitochondria during cyst formation. (A) Asymmetric fusome behavior during stem cell and cystocyte divisions. The fusome (red) remains in the stem cell (GSC) following mitosis (green, mitotic spindle; blue, chromosomes), while a smaller fusome grows in the cystoblast (CB) before cell separation is complete. The fusome branches during subsequent divisions that produce two-, four-, eight- and 16-cell cysts. The letters under each diagram correspond to figure panels illustrating the indicated stage. (B) A germline stem cell (broken circle) in G2 phase. Mitochondria (green) vary in length but most associate with the fusome (blue). Green, ATPsynthase; red, phalloidin; blue, 1B1. (C) Another GSC (broken circle), revealing the clustering of microtubules (green) around the fusome (red). Green, tubulin; red, 1B1; blue, DNA. (D) A mitotic GSC (broken circle). Round mitochondria associate with the outer region of the mitotic spindle (red) and segregate equally (see Table 1). Green, ATP synthase; red, tubulin; blue, DNA. (E) A stem cell (broken circle, left) and daughter cystoblast (broken circle, right) in S phase after mitosis remain connected via a ring canal (red) containing the fusome (blue). Mitochondria aggregate around the stem cell fusome (upper left), but show little or no association with the cystoblast fusome (lower right). Green, ATPsynthase; red, phalloidin; blue, 1B1. (F) Spherical mitochondria (green) within an eight-cell cyst (broken circle) do not associate with the fusome (blue). Green, ATPsynthase; red, phalloidin; blue, 1B1. (G) The anterior region of a living germarium labeled with Mitotracker to reveal the position and movement of mitochondria. Mitochondria in region 1 cysts do not associate with the fusome (arrowhead) while mitochondria in region 2 do (arrow). B-F are projections of multiple confocal z-sections. Scale bars: in F, 5 µm for B-F; 10 µm for G.

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