Dulovic Alex, Koch Iris, Hipp Katharina, Streit Adrian
Department of Integrative Evolutionary Biology, Max Planck Institute for Biology Tübingen, Max-Planck-Ring 5, 72076 Tübingen, Germany.
Electron Microscopy Facility, Max Planck Institute for Biology Tübingen, Max-Planck-Ring 5, 72076 Tübingen, Germany.
Mol Biochem Parasitol. 2022 Sep;251:111509. doi: 10.1016/j.molbiopara.2022.111509. Epub 2022 Aug 17.
If normal male meiosis occurs, it would be expected that 50 % of sperm lack an X chromosome (nullo X) and hence upon fertilisation, result in male progeny. However, for sexual reproduction within the free-living stages of Strongyloides spp. male offspring are absent. We had shown earlier by quantitative whole genome sequencing that within Strongyloides spp., nullo-X sperm are either absent (S. papillosus) or underrepresented (S. ratti) among mature sperm. To investigate how and when this elimination of male-determining sperm occurs, we characterised spermatogenesis and the dynamic localisation of important molecular players such as tubulin, actin and major sperm protein by DIC microscopy, immunohistochemistry, and fluorescent in situ hybridization (FISH) in S. ratti, S. papillosus and Parastrongyloides trichosuri. We found that meiotic divisions in these parasites proceeded as expected for organisms with XO males, resulting in four equally sized spermatocytes, two with and two without an X chromosome. However, mature sperm were found to almost always contain an X chromosome. We also observed structures that contained protein constituents of sperm, such as actin and major sperm protein (MSP) but no DNA. These structures resemble C. elegans residual bodies in appearance and may assume their function. We hypothesize that spermatocytes without an X-chromosome undergo some form of programmed cell death and transform into these residual body-like structures. As in C. elegans, MSP is found in fibrous body-membranous organelles (FB-MOs). Knocking down MSP by RNAi showed that MSP is essential for fertility in S. ratti, as it is in C. elegans.
如果正常的雄性减数分裂发生，预计50%的精子缺乏X染色体（无X染色体精子），因此受精后会产生雄性后代。然而，在粪类圆线虫属自由生活阶段的有性生殖过程中，雄性后代并不存在。我们之前通过定量全基因组测序表明，在粪类圆线虫属中，成熟精子中无X染色体精子要么不存在（乳头粪类圆线虫），要么数量较少（鼠粪类圆线虫）。为了研究这种决定雄性的精子是如何以及何时被消除的，我们通过微分干涉差显微镜、免疫组织化学和荧光原位杂交（FISH），对鼠粪类圆线虫、乳头粪类圆线虫和 Trichosuri副圆线虫的精子发生过程以及微管蛋白、肌动蛋白和主要精子蛋白等重要分子成分的动态定位进行了表征。我们发现，这些寄生虫的减数分裂过程与XO型雄性生物预期的一样，产生四个大小相等的精母细胞，其中两个含有X染色体，两个不含X染色体。然而，发现成熟精子几乎总是含有X染色体。我们还观察到一些结构，它们含有精子的蛋白质成分，如肌动蛋白和主要精子蛋白（MSP），但没有DNA。这些结构在外观上类似于秀丽隐杆线虫的残余体，可能承担其功能。我们假设，不含X染色体的精母细胞会经历某种形式的程序性细胞死亡，并转化为这些类似残余体的结构。与秀丽隐杆线虫一样，MSP存在于纤维体 - 膜细胞器（FB - MOs）中。通过RNA干扰敲低MSP表明，MSP对鼠粪类圆线虫的生育能力至关重要，就像在秀丽隐杆线虫中一样。
