Röper Katja, Brown Nicholas H
Wellcome Trust/Cancer Research UK Institute and Department of Anatomy, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QR, United Kingdom.
Curr Biol. 2004 Jan 20;14(2):99-110.
During Drosophila oogenesis a membranous organelle called the fusome has a key function in the establishment of oocyte fate and polarity, ultimately leading to the establishment of the major body axes of the animal. The fusome is necessary for the microtubule-driven restriction of markers of oocyte fate to the oocyte, but the mechanism by which the fusome organizes the microtubules is not known.
We have identified the spectraplakin Short stop (Shot) as a new component of the fusome. Spectraplakins are giant cytoskeletal linker proteins, with multiple isoforms produced from each gene. Shot is the sole spectraplakin in Drosophila. The phenotype caused by the absence of Shot is not similar to that of other components of the fusome but instead is similar to the absence of the downstream components that interact with microtubules: the dynein/dynactin-complex-associated proteins Egalitarian and BicaudalD. Shot is required for the association of microtubules with the fusome and the subsequent specification of the oocyte in 16-cell cysts. Shot is also required for the concentration of centrosomes into the oocyte, a process thought to be independent of microtubules because it still occurs in the presence of microtubule depolymerizing drugs. This suggests that Shot may protect some microtubules from depolymerization and that these microtubules are sufficient for this process.
Shot provides the missing link between the fusome and microtubules within meiotic cysts, which is essential for the establishment of the oocyte. Shot associates with the fusome and is required for microtubule organization. We suggest that it does this directly, via its microtubule binding GAS2 domain.
在果蝇卵子发生过程中，一种名为融合体的膜性细胞器在卵母细胞命运和极性的建立中起关键作用，最终导致动物主要体轴的形成。融合体对于微管驱动的将卵母细胞命运标记物限制在卵母细胞中是必需的，但融合体组织微管的机制尚不清楚。
我们已鉴定出光谱斑蛋白短停（Shot）是融合体的一种新成分。光谱斑蛋白是巨大的细胞骨架连接蛋白，每个基因产生多种异构体。Shot是果蝇中唯一的光谱斑蛋白。Shot缺失所导致的表型与融合体的其他成分不同，而是类似于与微管相互作用的下游成分缺失时的表型：动力蛋白/动力蛋白激活蛋白复合物相关蛋白平等主义者和双尾D。在16细胞囊肿中，微管与融合体的结合以及随后卵母细胞的特化需要Shot。卵母细胞中中心体的聚集也需要Shot，这一过程被认为与微管无关，因为在存在微管解聚药物的情况下它仍然会发生。这表明Shot可能保护一些微管不发生解聚，并且这些微管对于这一过程就足够了。
Shot提供了减数分裂囊肿中融合体与微管之间缺失的联系，这对于卵母细胞的形成至关重要。Shot与融合体相关联，并且是微管组织所必需的。我们认为它是通过其微管结合GAS2结构域直接做到这一点的。
