胞浆小滴可能是精子运动和正常精子形成的标志

哺乳动物生精过程后期精细胞胞浆脱落后，有一个微小部分经常会残留于精子鞭毛上，被称为胞浆小滴。胞浆小滴被认为在精子体积的调整中起到重要作用。然而，我们观察到含有胞浆小滴的精子大多显示出运动活力，而不含有胞浆小滴的精子则鲜有运动活力，说明在附睾成熟过程中胞浆小滴的存在对精子运动起重要作用。在本研究中，我们分析了小鼠及猴的精子在附睾成熟期间含有及不含有胞浆小滴的精子运动能力获得的关系，以及胞浆小滴在精子尾部位置的改变的关系。我们也检测了3种晚期精子生成缺陷基因敲除小鼠的精子胞浆小滴。我们的数据显示胞浆小滴是暂时存在于附睾精子上的正常附属器官，正常的胞浆小滴形态及位置与精子附睾成熟过程中正常的运动能力形成相关。胞浆小滴的异常形成，胞浆小滴的缺失或者异常的胞浆小滴预示着精子形成缺陷。如果胞浆小滴是精子运动形成的基础，那么胞浆小滴可以成为非激素类男性避孕药的理想的药物靶点。

The cytoplasmic droplet may be indicative of sperm motility and normal spermiogenesis

Although the cytoplasm of spermatids is removed at the end of spermiogenesis, a tiny portion is usually retained in the sperm flagellum, which is termed the cytoplasmic droplet （CD） in mammals. CDs are believed to play a role in sperm volume adaptation. However, we have noticed that epididymal spermatozoa that display initial （flagellation in situ） and progressive motility mostly possess CDs, whereas spermatozoa without CDs are rarely motile, suggesting that CDs have a role in motility development during sperm epididymal maturation. In the present study, we analyzed the relationship between the presence or absence of CDs, motility development and positional changes of CDs during sperm epididymal maturation in mice and monkeys. We also examined CDs on spermatozoa of three knockout mouse lines with late spermiogenic defects. Our data suggest that the CD is a normal organelle transiently present exclusively on epididymal spermatozoa, and normal CD morphology and location are associated with normal motility development during epididymal maturation of spermatozoa. Abnormal CD formation, e.g., a complete lack of CDs or ectopic CDs, is indicative of defective spermiogenesis. If CDs are essential for sperm motility development, then CDs may represent an ideal drug target for the development of non-hormonal male contraceptives.