Riparbelli Maria Giovanna, Callaini Giuliano, Mercati David, Hertel Horst, Dallai Romano
Department of Evolutionary Biology, University of Siena, Siena, Italy.
Cell Motil Cytoskeleton. 2009 May;66(5):248-59. doi: 10.1002/cm.20352.
In addition to their role in centrosome organization, the centrioles have another distinct function as basal bodies for the formation of cilia and flagella. Centriole duplication has been reported to require two alternate assembly pathways: template or de novo. Since spermiogenesis in the termite Mastotermes darwiniensis lead to the formation of multiflagellate sperm, this process represents a useful model system in which to follow basal body formation and flagella assembly. We present evidence of a possible de novo pathway for basal body formation in the differentiating germ cell. This cell also contains typical centrosomal proteins, such as centrosomin, pericentrin-like protein, gamma-tubulin, that undergo redistribution as spermatid differentiation proceeds. The spermatid centrioles are long structures formed by nine doublet rather than triplet microtubules provided with short projections extending towards the surrounding cytoplasm and with links between doublets. The sperm basal bodies are aligned in parallel beneath the nucleus. They consist of long regions close to the nucleus showing nine doublets in a cartwheel array devoid of any projections; on the contrary, the short region close to the plasma membrane, where the sperm flagella emerge, is characterized by projections similar to those observed in the centrioles linking the basal body to the plasma membrane. It is hypothesized that this appearance is in connection with the centriole elongation and further with the flagellar axonemal organization. Microtubule doublets of sperm flagellar axonemes are provided with outer dynein arms, while inner arms are rarely visible.
除了在中心体组织中发挥作用外，中心粒还具有另一个独特功能，即作为形成纤毛和鞭毛的基体。据报道，中心粒复制需要两种交替的组装途径：模板途径或从头合成途径。由于达尔文澳白蚁精子发生过程会形成多鞭毛精子，这一过程代表了一个有用的模型系统，可用于追踪基体形成和鞭毛组装。我们提供了分化中的生殖细胞中基体形成可能存在从头合成途径的证据。这种细胞还含有典型的中心体蛋白，如中心体蛋白、类中心粒外周蛋白、γ-微管蛋白，随着精子细胞分化的进行，这些蛋白会发生重新分布。精子细胞的中心粒是由九个双联体而非三联体微管形成的长结构，有短突起向周围细胞质延伸，双联体之间有连接。精子基体在细胞核下方平行排列。它们由靠近细胞核的长区域组成，呈车轮状排列，有九个双联体，没有任何突起；相反，靠近质膜的短区域，即精子鞭毛出现的地方，其特征是有类似于在中心粒中观察到的突起，将基体与质膜相连。据推测，这种外观与中心粒伸长以及进一步与鞭毛轴丝组织有关。精子鞭毛轴丝的微管双联体有外动力蛋白臂，而内臂很少可见。
