A comparative view of sperm ultrastructure.
A comparative view of sperm ultrastructure.
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DOI：
10.1095/biolreprod2.supplement_2.90
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发表时间：
1970-01-01
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影响因子：
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通讯作者：
Fawcett, D. W.
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文献类型：
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作者：
Fawcett, D. W.
体外受精动物的相对原始的精子有一个简单的运动装置，由一个简单的9 + 2鞭毛和一个围绕其基部的线粒体环组成。但与此同时，这些精子通常有高度特化的顶体，这些顶体经历复杂的反应，以确保精子接触并穿透卵子的保护涂层。在内部受精的动物中，如哺乳动物，顶体的特化程度较低，靠近卵子会引起一种反应，这种反应显然仅限于通过类似于分泌的过程释放溶解物质。另一方面，通过获得额外的外排纤维，运动器官已经适应了通过女性生殖道的进展，从而形成了熟悉的9 + 9 + 2模式。伴随这一变化的是线粒体数量的增加，它们形成一个长长的中间部分，显然是为了在更粘稠的介质中提供更大的运动能量需求。这些额外部件所带来的功率增加，必须在一定程度上被更大的内部抗弯曲阻力所抵消，这将不可避免地由增加的结构和精子近端部分的整体增厚所导致。本文描述的哺乳动物精子的比较研究揭示了一种共同的结构计划，但在外层纤维的厚度、中间部分的长度和尾部的总直径方面却存在令人惊讶的物种差异。有暗示的形态学证据表明，增加外层纤维的直径可以克服外部延迟力和内部弯曲阻力；通过使它们远离弯曲轴来增加它们的机械优势；通过添加第三阶电机元件，卫星纤维；或者通过这些装置的各种组合。通过对精子异常运动模式的电影分析，我们可以更多地了解到精子中所观察到的差异的功能意义，这些异常运动模式可能与特定结构成分的异常发育有关。对尾猴精子精细结构的研究表明，其轴向纤维与哺乳动物精子尾部的一种外层致密纤维同源，边缘纤维可能与纤维鞘的一根纵柱同源。在尾猿精子中，线粒体与轴突纤维的密切联系，而不是与轴突复合体的密切联系，这与轴突能够独立于线粒体能量来源发挥作用的解释是一致的，但脊椎动物精子的中间长段已经进化到满足附属外纤维的能量需求。
The relatively primitive spermatozoa of animals with external fertilization have an uncomplicated locomotor apparatus consisting of a simple 9 + 2 flagellum with a single ring of mitochondria around its base. But at the same time, these sperm often have highly specialized acrosomes that undergo complex reactions to insure that the sperm contacts and penetrates the protective coatings of the egg.In animals with internal fertilization, such as the mammals, the acrosome is less highly specialized and proximity to the egg elicits a response that is apparently limited to release of lytic substances by a process akin to secretion. The locomotor apparatus, on the other hand, has become adapted for progression through the female reproductive tract by acquiring an additional outer row of fibers, resulting in the familiar 9 + 9 + 2 pattern. Accompanying this change is an increase in number of mitochondria and their association to form a long middle piece, apparently to provide for the greater energy requirements of locomotion in a more viscous medium. The increase in power achieved by these additional components must be offset to some extent by the greater internal resistance to bending that would inevitably result from the structures added and from the overall thickening of the proximal segments of the sperm.The comparative studies of mammalian sperm described here reveal a common architectural plan but surprising species differences in thickness of the outer fibers, length of middle piece, and overall diameter of the tail. There is suggestive morphological evidence that both external retarding forces and internal resistance to bending are overcome by increasing the diameter of the outer fibers; by moving them farther from the axis of bending to increase their mechanical advantage; by addition of a third order of motor elements, the satellite fibers; or by various combinations of these devices. Much more might be learned about the functional significance of the observed differences in sperm from cinematographic analysis of unusual patterns of locomotion that may be correlated with exceptional development of particular structural components.Investigation of the fine structure of a urodele spermatozoon suggests that its axial fiber is the homolog of one of the outer dense fibers of the mammalian sperm tail and that the marginal fiber is probably homologous with one of the longitudinal columns of the fibrous sheath. The close association of the mitochondria with the axial fiber in urodele sperm, instead of with the axonemal complex, is consistent with the interpretation that the axoneme is capable of functioning rather independently of a mitochondrial energy source but that the long middle piece of vertebrate sperm has evolved to meet the energy requirements of the accessory outer fibers.