Lu Yonggang, Aitken Robert John, Lin Minjie
Priority Research Centre for Reproductive Science, School of Environmental and Life Sciences, Faculty of Science, University of Newcastle, Callaghan, New South Wales, Australia.
PLoS One. 2017 Apr 3;12(4):e0174907. doi: 10.1371/journal.pone.0174907. eCollection 2017.
For the first time, this study has systemically investigated the male reproductive system in a sessile broadcast-spawning marine invertebrate, Galeolaria caespitosa (Polychaeta: Serpulidae), which has significant potential as a bio-indicator species of coastal marine pollution. The abdomen of G. caespitosa was divided by intersegmental septa into over 80 trunk segments. Each segment served as a germinal chamber with a C-shaped gonadal arrangement consisting of several distinct compartments: a seminiferous epithelium (SE) compartment located in the centre of the chamber, with each of its two ends connecting to a nurse cell (NC) compartment and then an efferent duct (ED) compartment. The SE compartment contained a multilayered seminiferous epithelium where spermatogenesis was initiated. Spermatids were released in pairs into the lumen of the SE compartment and then transported to the NC compartment where they underwent spermiogenesis with the support of secretory vesicles released by the nurse cells. Spermatozoa were stored in the ED compartment and subsequently released into the seawater through the vas deferens. Unlike vertebrates where germ cells differentiated in close proximity to the nurse cell population (i.e. Sertoli cells), the spermatogenic cells of G. caespitosa exhibited no direct contact with supporting cells at any spermatogenic stage. This finding suggested that the spermatogenesis in G. caespitosa was more dependent on intrinsic developmental programming than most species. Notwithstanding such differences, there were clear parallels between the male reproductive system of G. caespitosa and mammals, in terms of the structure and function. The independence of spermatogenic cells from supporting cells in G. caespitosa raised the possibility of inducing spermiogenesis in vitro, which would provide a useful tool to dissect the mechanisms underlying this complex cell differentiation process in invertebrates and other higher order animals.
本研究首次系统地研究了固着型散播产卵海洋无脊椎动物苔藓虫（多毛纲：苔藓虫科）的雄性生殖系统，该物种作为沿海海洋污染的生物指示物种具有巨大潜力。苔藓虫的腹部被节间隔膜分成80多个躯干节段。每个节段作为一个生殖腔，具有C形性腺排列，由几个不同的部分组成：位于腔中心的生精上皮（SE）部分，其两端分别连接到一个滋养细胞（NC）部分，然后是一个输出管（ED）部分。SE部分包含多层生精上皮，精子发生在此启动。精子细胞成对释放到SE部分的管腔中，然后运输到NC部分，在那里它们在滋养细胞释放的分泌小泡的支持下进行精子形成。精子储存在ED部分，随后通过输精管释放到海水中。与生殖细胞在靠近滋养细胞群体（即支持细胞）处分化的脊椎动物不同，苔藓虫的生精细胞在任何精子发生阶段都不与支持细胞直接接触。这一发现表明，苔藓虫的精子发生比大多数物种更依赖于内在的发育程序。尽管存在这些差异，但苔藓虫的雄性生殖系统与哺乳动物在结构和功能方面有明显的相似之处。苔藓虫中生精细胞与支持细胞的独立性增加了体外诱导精子形成的可能性，这将为剖析无脊椎动物和其他高等动物这种复杂细胞分化过程的潜在机制提供一个有用的工具。
