BACKGROUND The calmodulin-regulated spectrin-associated proteins (CAMSAPs) belong to a conserved protein family, which includes members that bind the polymerizing mcrotubule (MT) minus ends and remain associated with the MT lattice formed by minus end polymerization. Only one of the three mammalian CAMSAPs, CAMSAP1, localizes to the mitotic spindle but its function is unclear. In Drosophila, there is only one CAMSAP, named Patronin. Previous work has shown that Patronin stabilizes the minus ends of non-mitotic MTs and is required for proper spindle elongation. However, the precise role of Patronin in mitotic spindle assembly is poorly understood. RESULTS Here we have explored the role of Patronin in Drosophila mitosis using S2 tissue culture cells as a model system. We show that Patronin associates with different types of MT bundles within the Drosophila mitotic spindle, and that it is required for their stability. Imaging of living cells expressing Patronin-GFP showed that Patronin displays a dynamic behavior. In prometaphase cells, Patronin accumulates on short segments of MT bundles located near the chromosomes. These Patronin "seeds" extend towards the cell poles and stop growing just before reaching the poles. Our data also suggest that Patronin localization is largely independent of proteins acting at the MT minus ends such as Asp and Klp10A. CONCLUSION Our results suggest a working hypothesis about the mitotic role of Patronin. We propose that Patronin binds the minus ends within MT bundles, including those generated from the walls of preexisting MTs via the augmin-mediated pathway. This would help maintaining MT association within the mitotic bundles, thereby stabilizing the spindle structure. Our data also raise the intriguing possibility that the minus ends of bundled MTs can undergo a limited polymerization.

中文翻译：

---

护Pat素在果蝇有丝分裂中的作用。

背景技术钙调蛋白调节的血影蛋白相关蛋白（CAMSAPs）属于保守的蛋白家族，其包括与聚合的微管（MT）负端结合并保持与由负端聚合形成的MT晶格缔合的成员。三种哺乳动物CAMSAP中只有一种CAMSAP1定位于有丝分裂纺锤体，但其功能尚不清楚。在果蝇中，只有一个CAMSAP，名为Patronin。先前的工作表明，Patronin可以稳定非有丝分裂MT的负端，并且对于正常的纺锤体伸长是必需的。但是，人们对Patronin在有丝分裂纺锤体组装中的确切作用了解甚少。结果在这里，我们以S2组织培养细胞为模型系统探索了Patronin在果蝇有丝分裂中的作用。我们显示，Patronin与果蝇有丝分裂纺锤体中不同类型的MT束相关联，这是其稳定性所必需的。表达Patronin-GFP的活细胞的成像显示Patronin显示出动态行为。在前中期细胞中，Patronin聚集在靠近染色体的MT束的短段上。这些Patronin的“种子”向细胞两极延伸，并在到达两极之前停止生长。我们的数据还表明，Patronin的定位很大程度上独立于在MT负端起作用的蛋白质，例如Asp和Klp10A。结论我们的结果提出了关于Patronin的有丝分裂作用的有效假设。我们建议守护神结合MT束内的负端，包括通过augmin介导的途径从先前存在的MT壁产生的那些。这将有助于在有丝分裂束中维持MT关联，从而稳定纺锤体结构。我们的数据还提出了一个有趣的可能性，即成束MT的负端可以进行有限的聚合。