The Gurdon Institute and the Department of Genetics, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK.
The University of Manchester, Manchester Academic Health Science Centre, Faculty of Biology, Medicine and Health, School of Biology, Manchester M13 9PT, UK.
Development. 2024 Apr 1;151(7). doi: 10.1242/dev.202370. Epub 2024 Apr 2.
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.
在果蝇中，只有一个细胞在一个多细胞雌性生殖细胞囊中被指定为卵母细胞，类似的过程也发生在哺乳动物中。卵母细胞选择的对称破缺线索是由纤毛体提供的，纤毛体是连接囊中的所有细胞的管状结构。果蝇spectraplakin Shot 定位于纤毛体，并将其不对称性转化为极化的微管网络，这对于卵母细胞的特化是必不可少的，但 Shot 如何识别纤毛体尚不清楚。在这里，我们证明 Shot 的肌动蛋白结合结构域 (ABD) 是将 Shot 定位到纤毛体所必需和充分的，并与微管结合结构域一起介导 Shot 在卵母细胞特化中的功能。Shot ABD 的钙调蛋白同源结构域 1 识别纤毛体 F-肌动蛋白，并且需要钙调蛋白同源结构域 2 将其与囊中的其他形式的 F-肌动蛋白区分开来。相比之下，utrophin、Fimbrin、Filamin、Lifeact 和 F-tractin 的 ABD 不识别纤毛体 F-肌动蛋白。因此，我们提出 Shot 通过识别纤毛体上 F-肌动蛋白的特定构象状态来传播纤毛体的不对称性。
