Abstract
In mammals and flies, only one cell in a multicellular female germline cyst becomes an oocyte, but how symmetry is broken to select the oocyte is unknown. Here we show that the microtubule minus end-stabilizing protein, Patronin/CAMSAP marks the future Drosophila oocyte and is required for oocyte specification. The spectraplakin, Shot, recruits Patronin to the fusome, a branched structure extending into all cyst cells. Patronin stabilizes more microtubules in the cell with most fusome. Our data suggest that this weak asymmetry is amplified by Dynein-dependent transport of Patronin-stabilized microtubules. This forms a polarized microtubule network, along which Dynein transports oocyte determinants into the presumptive oocyte. Thus, Patronin amplifies a weak fusome anisotropy to break symmetry and select one cell to become the oocyte.
Highlights
In many organisms, not all female germ cells develop into oocytes
In Drosophila, germline cyst formation starts in the germarium, which has 3 regions
As the cyst moves through regions 2a-b of the germarium, it is surrounded by epithelial follicle cells and rounds up in region 3 to form a follicle
Summary
Not all female germ cells develop into oocytes. Some cells become accessory cells that contribute material to the oocyte [1]. Oocyte selection depends on the formation of a noncentrosomal microtubule organizing center (ncMTOC) in the future oocyte that organizes a polarized microtubule network that directs the dynein-dependent transport of cell fate determinants and centrosomes into the pro-oocyte [6,7,8] (Fig. 1A). Patronin starts to accumulate in a single cell in each cyst in region 2a, earlier than other markers for the presumptive oocyte, and remains in one cell in regions 2b-3, where it forms distinct foci in the cytoplasm (Fig. 2A-2A’).
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