Riparbelli Maria Giovanna, Migliorini Massimo, Callaini Giuliano
Department of Life Sciences, University of Siena, Siena, Italy.
Cytoskeleton (Hoboken). 2025 Aug;82(8):516-528. doi: 10.1002/cm.21986. Epub 2025 Jan 3.
We analysed here the dynamic of the kinesin-like Pavarotti (Pav) during male gametogenesis of wild-type and Sas4 mutant flies. Pav localizes to the equatorial region and the inner central spindle of late anaphase wild-type spermatogonia and displays a strong concentration at the midbody during late telophase. At metaphase of the first meiotic division, Pav shows widespread localization on the equatorial region of the spermatocytes. This unusual distribution restricts and enhances during anaphase where antiparallel cortical microtubules overlap. Additional Pav staining is also found in the inner central spindle where the microtubules overlap between the segregating chromosomes. At late telophase, Pav accumulates to the midbody and on a weak ring that surround the cytoplasmic bridges. Pav localizes in an equatorial discontinuous ring of Sas4 spermatogonia where the non-centrosomal microtubules overlap, but the motor protein is absent in the interior central spindle where the inner microtubules are lacking. However, the anastral spindles properly support cell division, suggesting that astral microtubules are dispensable for Pav localization in the Sas4 spermatogonial cell cortex. This function is presumably replaced by the antiparallel cortical microtubules extending from the acentriolar polar regions. In contrast, the majority of the meiotic spindles in Sas4 mutant testes do not progress beyond late anaphase, and only a small fraction of the primary spermatocytes experienced an abnormal division with the assembly of aberrant telophase spindles. Pav accumulates around the chromatin clusters or enhanced at the plus ends of the antiparallel non-centrosomal cortical bundles of microtubules. However, these bundles are not arranged properly in the equatorial region of the cell and cytokinesis is abnormal or fails. Therefore, the observations in Sas4 mutant testes suggest that the spermatogonial mitoses correctly occur in the absence of astral microtubules, whereas meiotic divisions fail.
我们在此分析了野生型和Sas4突变果蝇雄性配子发生过程中类驱动蛋白Pavarotti（Pav）的动态变化。Pav定位于后期野生型精原细胞的赤道区域和内中央纺锤体，并在末期后期在中体处高度富集。在第一次减数分裂中期，Pav广泛定位于精母细胞的赤道区域。这种不寻常的分布在后期反平行皮质微管重叠时受到限制并增强。在分离染色体之间微管重叠的内中央纺锤体中也发现了额外的Pav染色。在末期后期，Pav聚集到中体以及围绕细胞质桥的弱环上。Pav定位于Sas4精原细胞赤道不连续环中，此处非中心体微管重叠，但在缺乏内部微管的内中央纺锤体中不存在驱动蛋白。然而，无星纺锤体正确支持细胞分裂，表明星状微管对于Pav在Sas4精原细胞皮质中的定位是可有可无的。该功能可能由从无中心粒极区延伸的反平行皮质微管取代。相比之下，Sas4突变睾丸中的大多数减数分裂纺锤体不会超过后期后期，只有一小部分初级精母细胞经历异常分裂并组装异常的末期纺锤体。Pav聚集在染色质簇周围或在反平行非中心体皮质微管束的正端增强。然而，这些束在细胞赤道区域排列不正确，胞质分裂异常或失败。因此，在Sas4突变睾丸中的观察结果表明，在没有星状微管的情况下精原细胞有丝分裂正确发生，而减数分裂失败。
