Key Laboratory of Insect Developmental and Evolutionary Biology, Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, 200032, Shanghai, China; University of Chinese Academy of Sciences, 100049, Beijing, China.
Key Laboratory of Insect Developmental and Evolutionary Biology, Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, 200032, Shanghai, China.
Insect Biochem Mol Biol. 2022 Dec;151:103874. doi: 10.1016/j.ibmb.2022.103874. Epub 2022 Nov 12.
In lepidopteran insects, sperm dimorphism is a remarkable feature, in which males exhibit two different types of sperms. Both sperm morphs are essential for fertilization: Eupyrene sperm carry DNA and fertilize eggs, whereas apyrene sperm, which do not have nuclei, are necessary for transport of eupyrene sperm into eggs. In this study, we showed that the gene BmHen1, which encodes a methyltransferase that modifies piRNAs, is necessary for eupyrene sperm development in the lepidopteran model insect, Bombyx mori. Loss-of-function mutants of BmHen1 of both sexes were sterile. BmHen1 female mutants laid fewer eggs than wild-type females, and the eggs laid had morphological defects. Immunofluorescence analysis of BmHen1 male mutants revealed that nuclei formation in the eupyrene sperm was defective, whereas apyrene sperm were normal. In mice, worms, and flies, the components in piRNA biogenesis pathway play an important role in gonad development; therefore, we constructed mutations in genes encoding core elements in the piRNA biogenesis pathway, Siwi, and BmAgo3. To our surprise, no obvious phenotypes were observed in the male reproduction system in the Siwi and BmAgo3 mutants, which demonstrated that sperm development in B. mori does not depend on piRNAs. As the sperm development phenotype in BmHen1 mutants mimics the phenotype of the BmPnldc1 mutants, we then performed RNA sequencing analysis of sperm bundles from both mutants. We found that the defects in eupyrene sperm resulted from dysregulation of the expression of genes involved in energy metabolism. Taken together, our findings demonstrate the crucial functions of BmHen1 in the development of eupyrene sperm and provide evidence that spermatogenesis in B. mori is PIWI-independent. Our results suggest potential targets for lepidopteran pest control and broaden our knowledge of the reproduction in this order of insects.
在鳞翅目昆虫中，精子二态性是一个显著的特征，其中雄性表现出两种不同类型的精子。两种精子形态都对受精至关重要：有核精子携带 DNA 并使卵子受精，而无核精子虽然没有细胞核，但对于有核精子进入卵子的运输是必要的。在这项研究中，我们表明，编码一种修饰 piRNA 的甲基转移酶的基因 BmHen1 对于鳞翅目模式昆虫家蚕的有核精子发育是必要的。BmHen1 的雌雄功能丧失突变体均不育。BmHen1 雌性突变体产卵量少于野生型雌性，所产卵具有形态缺陷。BmHen1 雄性突变体的免疫荧光分析表明，有核精子的核形成有缺陷，而无核精子正常。在小鼠、蠕虫和果蝇中，piRNA 生物发生途径中的成分在性腺发育中起着重要作用；因此，我们构建了编码 piRNA 生物发生途径核心元件的基因 Siwi 和 BmAgo3 的突变体。令我们惊讶的是，Siwi 和 BmAgo3 突变体的雄性生殖系统没有明显的表型，这表明家蚕的精子发育不依赖于 piRNA。由于 BmHen1 突变体的精子发育表型类似于 BmPnldc1 突变体的表型，我们随后对来自两种突变体的精子束进行了 RNA 测序分析。我们发现，有核精子的缺陷是由于参与能量代谢的基因表达失调所致。综上所述，我们的研究结果表明 BmHen1 在有核精子发育中的关键作用，并提供了家蚕精子发生不依赖于 PIWI 的证据。我们的研究结果为鳞翅目害虫的防治提供了潜在的靶点，并拓宽了我们对这一昆虫目繁殖的认识。
