Aquaporins are expressed in the columnar cells of the midgut epithelium of the silkworm, <i>Bombyx mori</i>

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  • Maruyama Mariya
    Laboratory of Insect Physiology, The United Graduate School of Agricultural Sciences, Tottori University
  • Azuma Masaaki
    Laboratory of Insect Physiology, The United Graduate School of Agricultural Sciences, Tottori University

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  • Aquaporins are expressed in the columnar cells of the midgut epithelium of the silkworm, Bombyx mori

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Abstract

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.<br>

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