Molecular physiological studies on insect excretion and water regulation and its application -physiology of aquaporin and its disorder-

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Epithelial and cellular mechanisms in water transport has been explored over 50 years. Knowledge on the molecular aspects of water regulation in living organisms has greately increased in recent years. Water transport across the plasma membrane depends on the presence of water channel-aquaporin (AQP). Studies on water transport itself in insect epithelia is so far lacking, although the movement of ions and water are inextricably linked. There are still few physiological studies on the multiple functions of AQP in insect epithelia. This project set out to investigate the present status on our understanding of insect aquaporins and the recent advances in the molecular and cellular roles of caterpillar's AQP.Currently, all insect AQPs are water-specific except for the caterpillar's AQP, which possess the other isoform which enables to transport glycerol and urea (aquaglyceroporin : GLP). Water-specific AQPs in insects are classified into two closely related subfamilies, called DRIP (Drosophila Intrinsic Protein) and PRIP (Pyrocoelia rufa Intrinsic Protein) phylogenetically. Insect AQPs in very recent reports fall into DRIP or PRIP. In the silkworm, Bombyx mori, we have identified these three types, i.e., AQP-Bom1 as DRIP-type, Bom2 as GLP-type, Bom3 as PRIP-type. Caterpillars (solid/plant feeder) are normally endurable against drought and starvation compare to the liquid/plant feeders such as a leafhopper. Therefore, these three AQPs of B. mori, collaborate to maintain not only water balance, but also excretion in silkworm larvae.