BACKGROUND Sperm morphology mainly refers to the shape of the head, the length of the flagellar segments, including the midpiece, principal piece and end piece, and the size of the accessory structures, including axonemes, outer dense fibers (ODFs), mitochondrial sheath (MS) and fibrous sheath (FS). Across species, there is considerable diversity in morphology. An established theory posits that the length of the sperm flagellum, especially the length of the midpiece, is a critical factor influencing sperm metabolism and velocity. However, our understanding of the relationships between sperm ultrastructures and the sperm flagellar length is incomplete. METHODS The morphologies of sperm from 10 mammalian species, human, mouse, rat, dog, rabbit, goat, pig, bull, guinea pig and golden hamster, were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). According to the SEM and TME images, the length of sperm heads and flagellar segments, the cross-sectional areas of the accessory structures and flagella and the width of sperm heads were measured using Image J software. The variation tendencies (referred to as slope) of the accessory structures along flagella were calculated by the linear regression method. Mitochondrial functions were measured using commercial kits. The velocities of sperm were measured using CASA software. RESULTS The three-dimensional morphologies of sperm from 10 species and the slopes of internal accessory structures along flagella were obtained. The width of the axoneme tapered slightly from the base to the tip of the sperm flagellum, and slopes of the axonemes correlated negatively with the variability in flagellar length across species. Additionally, the cross-sectional areas of the ODFs and/or the MS were positively correlated with the lengths of the midpiece, principal piece, and total flagellum, as well as with sperm velocities. Mitochondrial volumes were positively correlated with ATP content and sperm swimming velocities. CONCLUSIONS Our results not only show the relationship between sperm internal structures, flagellar length and sperm physiology but also provide sizes of mitochondria and ODFs as new targets with which to study the regulation of sperm length and velocity.

中文翻译：

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哺乳动物精子超微结构的比较分析揭示了精子形态，线粒体功能和运动性之间的关系。

背景技术精子形态主要是指头部的形状，鞭毛节段的长度（包括中段，主体段和末端段）以及附属结构的尺寸，包括轴突，外部致密纤维（ODF），线粒体鞘（ MS）和纤维鞘（FS）。跨物种，形态上有相当大的多样性。一个既定的理论认为，精子鞭毛的长度，特别是中段的长度，是影响精子代谢和速度的关键因素。但是，我们对精子超微结构和精子鞭毛长度之间关系的理解是不完整的。方法：从人，小鼠，大鼠，狗，兔，山羊，猪，公牛，豚鼠和金仓鼠等10种哺乳动物的精子形态上，通过扫描电子显微镜（SEM）和透射电子显微镜（TEM）检查。根据SEM和TME图像，使用Image J软件测量精子头和鞭毛节段的长度，附件结构和鞭毛的横截面积以及精子头的宽度。通过线性回归方法计算了沿鞭毛的附属结构的变化趋势（称为斜率）。使用商业试剂盒测量线粒体功能。使用CASA软件测量精子的速度。结果获得了10种精子的三维形态学和鞭毛内部附属结构的斜率。轴突的宽度从精子鞭毛的基部到尖端略微变细，轴突的斜率与跨物种鞭毛长度的变化呈负相关。此外，ODF和/或MS的横截面积与中段，主要段和总鞭毛的长度以及精子速度呈正相关。线粒体体积与ATP含量和精子游泳速度呈正相关。结论我们的结果不仅显示了精子内部结构，鞭毛长度和精子生理之间的关系，而且还提供了线粒体和ODF的大小作为研究精子长度和速度调节的新目标。主要部分，总鞭毛，以及精子速度。线粒体体积与ATP含量和精子游泳速度呈正相关。结论我们的结果不仅显示了精子内部结构，鞭毛长度和精子生理之间的关系，而且还提供了线粒体和ODF的大小作为研究精子长度和速度调节的新目标。主要部分，总鞭毛，以及精子速度。线粒体体积与ATP含量和精子游泳速度呈正相关。结论我们的结果不仅显示了精子内部结构，鞭毛长度和精子生理之间的关系，而且还提供了线粒体和ODF的大小作为研究精子长度和速度调节的新目标。