Molecular Characterization and Tissue Distribution of Mitochondrial Ca2+-Dependent Solute Carrier Protein during Prevention of Diapause by HCl Treatment in the Silkworm,Bombyx mori

Molecular Characterization and Tissue Distribution of Calcineurin Regulatory B Subunit during the Prevention of Diapause in the Silkworm, Bombyx mori

To clarify the molecular mechanism of prevention of entry into diapause in Bombyx mori by HCl treatment, we biochemically analyzed calcineurin regulatory B subunit (CNB) in diapause eggs treated with HCl solution. Our previous studies revealed that HCl treatment causes Ca²⁺ to efflux from diapause eggs. Therefore, we attempted to analyze CNB, which is known to associate with Ca²⁺. The gene expression level of CNB was increased by HCl treatment and the changes of the gene expression were almost the same as that in the non-diapause eggs. As for diapause eggs, almost no gene expression of CNB was confirmed except just after oviposition. In the assay for phosphorylation by protein kinase CK2, recombinant CNB (rCNB) was phosphorylated in vitro. Additionally, a Ca²⁺ binding assay indicated that rCNB shows affinity for Ca²⁺. The distribution of CNB was investigated with an immunohistochemical technique using antiserum against rCNB in diapause eggs and HCl-treated diapause eggs. CNB was localized in serosa cells and yolk cells in both eggs. These data may suggest that CNB is activated by intracellular Ca²⁺ or efflux Ca²⁺ resulting from HCl treatment, and that it plays a role in the molecular mechanisms of artificial diapause prevention or the breaking of diapause in the silkworm.

Proliferation characteristics of the intracellular microsporidian pathogen Nosema bombycis in congenitally infected embryos

Nosema bombycis is an obligate intracellular pathogen that can be transmitted vertically from infected females to eggs, resulting in congenital infections in embryos. Here we investigated the proliferation characteristics of N. bombycis in silkworm embryos using a histopathological approach and deep RNA sequencing. We found that N. bombycis proliferated mainly around yolk granules at the early stage of the embryonic development, 1-2 days post oviposition (dpo). At 4-6 dpo, a portion of N. bombycis in different stages adjacent to the embryo were packaged into the newly formed intestinal lumen, while the remaining parasites continued to proliferate around yolk granules. In the newly hatched larvae (9 dpo), the newly formed spores accumulated in the gut lumen and immediately were released into the environment via the faeces. Transcriptional profiling of N. bombycis further confirmed multiplication of N. bombycis throughout every stage of embryonic development. Additionally, the increased transcriptional level of spore wall proteins and polar tube proteins from 4 dpo indicated an active formation of mature spores. Taken together, our results have provided a characterization of the proliferation of this intracellular microsporidian pathogen in congenitally infected embryos leading to vertical transmission.