Sperm, which have a vital role in sexual reproduction in the animal kingdom, can display heteromorphism in some species. The regulation of sperm dichotomy remains a longstanding puzzle even though the phenomenon has been widely documented for over a century. Here we use Bombyx mori as a model to study a form of sperm dimorphism (eupyrene and apyrene sperm), which is nearly universal among Lepidoptera. We demonstrate that B. mori Sex-lethal (BmSxl) is crucial for apyrene sperm development, and that B. mori poly(A)-specific ribonuclease-like domain-containing 1 (BmPnldc1) is required for eupyrene sperm development. BmSXL is distributed in the nuclei and cytoplasm of somatic cyst cells in a mesh-like pattern and in the cytoplasm of germ cells enclosed in spermatocysts and sperm bundles. Cytological analyses of dimorphic sperm in BmSxl mutants (∆BmSxl) showed deficient apyrene sperm with abnormal nuclei, as well as loss of motility associated with malformed mitochondrial derivatives. We define the crucial function of apyrene sperm in the process of fertilization as assisting the migration of eupyrene spermatozoa from bursa copulatrix to spermatheca. By contrast, BmPnldc1 deficiency (∆BmPnldc1) caused eupyrene sperm abnormalities and impaired the release of eupyrene sperm bundles during spermiation. Although apyrene or eupyrene sperm defects impaired fertility of the mutated males, double copulation of a wild-type female with ∆BmSxl and ∆BmPnldc1 males could rescue the sterility phenotypes induced by single copulation with either gene-deficient male. Our findings demonstrate the crucial functions of BmSxl and BmPnldc1 in the development of sperm dimorphism and the indispensable roles of nonfertile apyrene sperm in fertilization.

精子在动物界的有性生殖中发挥着至关重要的作用，在某些物种中可以表现出异形性。尽管精子二分法的调节已被广泛记录了一个多世纪，但它仍然是一个长期存在的难题。在这里，我们使用家蚕作为模型来研究一种精子二态性（丁芘和芘精子），这在鳞翅目动物中几乎是普遍存在的。我们证明，B. mori Sex-lethal ( BmSxl ) 对于 apyrene 精子发育至关重要，并且B. mori poly(A) 特异性核糖核酸酶样结构域包含 1 ( BmPnldc1 ) 对于 apyrene 精子发育是必需的。BmSXL以网状分布于体细胞囊肿细胞的细胞核和细胞质中，以及精囊和精子束内的生殖细胞的细胞质中。BmSxl突变体 (Δ BmSxl )中二态性精子的细胞学分析显示，有缺陷的 apyrene 精子具有异常的细胞核，以及与畸形线粒体衍生物相关的运动性丧失。我们将芘精子在受精过程中的关键功能定义为协助芘精子从交配囊迁移到受精囊。相比之下，BmPnldc1缺陷 (Δ BmPnldc1 ) 会导致尤比林精子异常，并在精子形成过程中损害尤比林精子束的释放。尽管芘或真芘精子缺陷损害了突变雄性的生育能力，但野生型雌性与 Δ BmSxl和 Δ BmPnldc1雄性的双重交配可以挽救与任一基因缺陷雄性单次交配引起的不育表型。我们的研究结果证明了BmSxl和BmPnldc1在精子二态性发展中的关键功能以及非生育阿芘精子在受精中不可或缺的作用。