Asano Atsushi, Tajima Atsushi
Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8572, Japan.
Adv Exp Med Biol. 2017;1001:59-73. doi: 10.1007/978-981-10-3975-1_4.
Terminally differentiated avian sperm consist of a head which male genetic material locates and flagellum that provides the motive force to propel them towards the fertilization site. The apical end of the sperm head accommodates a secretory vesicle, called an acrosome, that undergoes acrosome reaction releasing proteolytic content to penetrate the peri-vitelline membrane of an egg. Transcriptionally and translationally inactive, sperm need to rely on these distinct compartments in which different functions are preassembled, in order to achieve the goal of "fertilization". How are these complex structures with high functionality formed? Spermatogenesis is divided into an early stage in which diploid spermatogonia is proliferated into round spermatids thorough mitotic and meiotic divisions, and a late stage in which round spermatids are transformed into sperm though nuclear condensation and elongation of the sperm head, and formation of accessory structures. Recently, it was reported in aves that morphologically differentiated sperm undergo post-testicular maturation during passage through the male genital tract, suggesting that a similar system to mammals might be involved in the acquisition of fertilizing ability in avian sperm. Investigation for mechanisms underlying how sperm regulate their functions which are necessary to achieve fertilization is important for developing reproductive biotechnology in aves, because cryopreservation of poultry sperm is still not reliable for use in commercial production or for the preservation of genetic resources. In this review, we firstly provide an update on avian spermatogenesis, and then discuss the uniqueness of structure and functions of avian sperm, highlighting differences from mammalian sperm. Lastly, we discuss the molecular mechanism and current techniques of cryopreservation for avian sperm.
终末分化的鸟类精子由头部和鞭毛组成，雄性遗传物质位于头部，鞭毛提供动力将精子推向受精部位。精子头部的顶端容纳一个分泌囊泡，称为顶体，顶体发生顶体反应，释放蛋白水解成分以穿透卵的卵周膜。精子在转录和翻译上均无活性，需要依赖这些预先组装了不同功能的独特区室，以实现“受精”的目标。这些具有高功能性的复杂结构是如何形成的呢？精子发生分为早期和晚期，早期二倍体精原细胞通过有丝分裂和减数分裂增殖为圆形精子细胞，晚期圆形精子细胞通过细胞核浓缩、精子头部延长以及附属结构的形成而转变为精子。最近有报道称，在鸟类中，形态学上分化的精子在通过雄性生殖道的过程中会经历睾丸后成熟，这表明鸟类精子受精能力的获得可能涉及与哺乳动物类似的系统。研究精子如何调节其受精所需功能的机制，对于发展鸟类生殖生物技术很重要，因为家禽精子的冷冻保存用于商业生产或遗传资源保存仍不可靠。在这篇综述中，我们首先介绍鸟类精子发生的最新情况，然后讨论鸟类精子结构和功能的独特性，突出与哺乳动物精子的差异。最后，我们讨论鸟类精子冷冻保存的分子机制和当前技术。
