Abstract
Cellular immunity in insects is accompanied by change in hemocyte shape. This study hypothesizes that cytoskeletal rearrangement is accompanied by transmembrane water transport to change cell volume, thus changing cell shape. A water-transporting pore (=aquaporin:AQP) has been identified in the beet armyworm, Spodoptera exigua. Its expression was detected in all developmental stages and tissues, although its transcription levels were different between biotic and abiotic conditions. Heterologous expression of Se-AQP in Sf9 cells showed that Se-AQP was localized on cell membrane. RNA interference (RNAi) using double-stranded RNA effectively suppressed its transcript levels. Under different ionic concentrations, hemocytes of RNAi-treated larvae did not change cell volume presumably due to malfunction in water transportation. Se-AQP might participate in glycerol transport because up-regulation of hemolymph glycerol titer after rapid cold-hardening was prevented by RNAi treatment against Se-AQP expression. The inhibitory effect of RNAi treatment on change of cell shape significantly impaired cellular immune responses such as phagocytosis and nodule formation upon bacterial challenge. RNAi treatment also significantly interfered with immature development of S. exigua. These results indicate that Se-AQP plays a crucial role in cell shape change that is required for cellular immunity and other physiological processes.
Highlights
Aquaporins (AQPs) belong to major intrinsic proteins that form a diverse family consisting of more than 1,700 integral membrane proteins
PPO is synthesized from a specific hemocyte, oenocytoid, and released into plasma by cell lysis in beet armyworm, Spodoptera exigua[26]
The present study hypothesize that AQP activity is required for cell volume change of hemocytes to perform cellular immune responses
Summary
Aquaporins (AQPs) belong to major intrinsic proteins that form a diverse family consisting of more than 1,700 integral membrane proteins They are responsible for transporting water and other neutral molecules through lipid bilayer membrane in almost all living organisms[1]. Phylogenetic analyses on insect AQPs have revealed the presence of six major subfamilies, including water/urea-transporting Pyrocoelia rufa integral proteins (PRIP), water-specific Drosophila intrinsic protein (DRIP), water and glycerol transporting aquaglyceroporin (Glp), glycerol-permeating entomoglyceroporin (Eglp), water-impermeable but cation-permeable Big Brain proteins (BIB), and unorthodox aquaporin (AQP12L)[8]. Various roles of AQPs in mammalian systems have been reported Besides their water transportation activity, they play crucial roles in cell migration, cell proliferation, and adipocyte metabolism[9]. Hemocyte-spreading behavior may need cell volume change by bidirectional water transportation. The present study hypothesize that AQP activity is required for cell volume change of hemocytes to perform cellular immune responses
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