Maelstrom regulates spermatogenesis of the silkworm, Bombyx mori.

The spermatogenesis of animal is essential for the reproduction and a very large number of genes participate in this procession. The Maelstrom (Mael) is identified essential for spermatogenesis in both Drosophila and mouse, though the mechanisms appear to differ. It was initially found that Mael gene is necessary for axis specification of oocytes in Drosophila, and recent studies suggested that Mael participates in the piRNA pathway. In this study, we obtained Bombyx mori Mael mutants by using a binary transgenic CRISPR/Cas9 system and analyzed the function of Mael in B. mori, a model lepidopteran insect. The results showed that BmMael is not necessary for piRNA pathway in the ovary of silkworm, whereas it might be essential for transposon elements (TEs) repression in testis. The BmMael mutation resulted in male sterility, and further analysis established that BmMael was essential for spermatogenesis. The spermatogenesis defects occurred in the elongation stage and resulted in nuclei concentration arrest. RNA-seq and qRT-PCR analyses demonstrated that spermatogenesis defects were associated with tight junctions and apoptosis. We also found that BmMael was not involved in the silkworm sex determination pathway. Our data provide insights into the biological function of BmMael in male spermatogenesis and might be useful for developing novel methods to control lepidopteron pests.