The Shot CH1 domain recognises a distinct form of F-actin during Drosophila oocyte determination
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In Drosophila, only one cell in a multicellular female germline cyst is specified as an oocyte and a similar process occurs in mammals. The symmetry-breaking cue for oocyte selection is provided by the fusome, a tubular structure connecting all cells in the cyst. The Drosophila spectraplakin Shot localises to the fusome and translates its asymmetry into a polarised microtubule network that is essential for oocyte specification, but how Shot recognises the fusome is unclear. Here, we demonstrate that the actin-binding domain (ABD) of Shot is necessary and sufficient to localise Shot to the fusome and mediates Shot function in oocyte specification together with the microtubule-binding domains. The calponin homology domain 1 of the Shot ABD recognises fusomal F-actin and requires calponin homology domain 2 to distinguish it from other forms of F-actin in the cyst. By contrast, the ABDs of utrophin, Fimbrin, Filamin, Lifeact and F-tractin do not recognise fusomal F-actin. We therefore propose that Shot propagates fusome asymmetry by recognising a specific conformational state of F-actin on the fusome.
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Peer reviewed: True
Acknowledgements: We are grateful to Jean-René Huynh, Christian Klämbt, Thomas Lecuit, Katja Röper and the Bloomington Drosophila Stock Center (NIH P40OD018537) for fly stocks; Nicola Lawrence at the Gurdon Institute Imaging Facility for assistance with microscopy; and John Overton for technical assistance in making transgenic flies.
Publication status: Published
Funder: Wellcome; doi: http://dx.doi.org/10.13039/100010269
Funder: University of Cambridge; doi: http://dx.doi.org/10.13039/501100000735
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Cancer Research UK (A14492, A24823)
Biotechnology and Biological Sciences Research Council (BB/R001618/1, BB/M007553/1, BB/I002448/1, BB/C515998/1)