In this study, we investigated the expression and localization of aquaporins (AQPs) in the midgut of the silkworm Bombyx mori, in order to elucidate their functions, and found that AQP-Bom1, a homologue of the water-specific Drosophila AQP [Drosophila integral protein (DRIP)], and AQP-Bom2, an aquaglyceroporin (GLP) subtype are mainly expressed in the middle and posterior midgut. In situ hybridization studies using digoxigenin-labelled RNA probes derived from an open reading frame of each AQP revealed that AQP mRNA is present in the columnar cells of the middle and posterior midgut. Immunohistochemical studies using an antipeptide antibody against each AQP molecule revealed that the positive reaction was localized at the apical surface of the columnar cells. However, H⁺-translocating vacuolar-type ATPase (H⁺ V-ATPase) was specifically immunolocalized to the goblet cell apical membranes in the middle and posterior midgut. This suggests that the columnar cells are responsible for water movement in the midgut. As AQP-Bom2 is a GLP that transports glycerol and urea, and is mostly distributed in the posterior midgut, AQP-Bom2 functions together with AQP-Bom1 as a water-specific AQP subtype found along the length of the midgut. An osmoregulatory network of AQPs enables the silkworm larvae to pool and maintain luminal wetness in the midgut using water taken in during feeding.

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Cytosolic sulfotransferases (SULTs) are enzymes that play important roles in the detoxification of xenobiotics, as well as in the modulation of endogenous compounds such as steroid hormones by sulfation. In this study, we identified a novel SULT, designated bmSULT, from the silkworm, Bombyx mori. A cDNA encoding bmSULT was cloned by employing the reverse transcriptase-polymerase chain reaction technique. The deduced amino acid sequence of bmSULT showed conserved residues and sequence homology to known SULTs. Quantitative real-time PCR revealed that bmSULT mRNA was abundant in the larval midgut and pupal fat body of B. mori.

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We isolated and analyzed entomopathogenic microsporidia from the common cutworm, which were surveyed in vegetable crop fields on Chichijima, Ogasawara Islands, Japan, from April 2012 to March 2014. The infection rate of of the Spodoptera litura by microsporidia was 3.54% (161 of the 4,544 surveyed S. litura adults). In addition, 10 discrete strains of microsporidia collected from infected adults were measured for spore size and analyzed at the molecular level.
Analysis of the spore sizes indicated that the 10 strains of microsporidia isolated from the Ogasawara Islands comprised several different genera. Furthermore, analysis of the small-subunit ribosomal RNA sequences revealed that several microsporidian strains isolated from S. litura were closely related to Nosema bombycis from the silkworm Bombyx mori. Other microsporidia belonged to the Pleistophora and Trachipleistophora clusters. Therefore, the Ogasawara strains did not form a single genus group but were classified into at least 3 groups. This is the first study to identify the genus Trachipleistophora in lepidopteran insects in Japan. These results suggest that the microsporidia isolated from S. litura in the Ogasawara islands are genetically diverse.

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