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bioRxiv · 10.1101/2021.01.31.429051

β-importins Tnpo-SR and Cadmus and the small GTPase Ran promote ovarian cyst formation in Drosophila

Beachum, A. N.·Hinnant, T. D.·Williams, A. E.·Powell, A. M.·Ables, E. T.
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Abstract

Germ cells undergo mitotic expansion via incomplete cytokinesis, forming cysts of undifferentiated cells that remain interconnected prior to meiotic initiation, through mechanisms that are not well-defined. In somatic cells, Ras-related nuclear protein (Ran) spatiotemporally regulates mitotic spindle assembly, cleavage furrow formation and abscission. Here, we identify Ran and {beta}-importins as critical regulators of cyst development in the Drosophila ovary. Depletion of Ran or the {beta}-importins Tnpo-SR and cadmus disrupts oocyte selection and results in egg chambers with variable numbers of germ cells, suggesting abnormal cyst development and cyst fragmentation. We demonstrate that Ran, Tnpo-SR, and Cadmus regulate key cellular processes during cyst formation, including cell cycle dynamics, fusome biogenesis, and ring canal stability, yet do so independently of mitotic spindle assembly. Further, Tnpo-SR and Cadmus control cyclin accumulation and suppress cytokinesis independent of Ran-GTP, suggesting that {beta}-importins sequester protein cargos that normally promote the mitotic-to-meiotic transition. Our data demonstrates that Ran and {beta}-importins are critical for germ cell cyst formation, a role that is likely conserved in other organisms. SUMMARY STATEMENTRan and two {beta}-importins function coordinately to promote oocyte selection and cyst development in the Drosophila ovary.

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Beachum, A. N., Hinnant, T. D., Williams, A. E., Powell, A. M., Ables, E. T.. 2021-02-01. β-importins Tnpo-SR and Cadmus and the small GTPase Ran promote ovarian cyst formation in Drosophila. https://doi.org/10.1101/2021.01.31.429051

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