Identification and functional characterization of an ovarian aquaporin from the 1 cockroach

quantitative real time PCR; REST, relative expression software tool. 31 32 2 SUMMARY 33 Aquaporins (AQPs) are membrane proteins that form water channels, allowing rapid 34 movement of water across cell membranes. AQPs have been reported in species of all 35 life kingdoms and in almost all tissues, but little is known about them in insects. Our 36 purpose was to explore the occurrence of AQPs in the ovary of the phylogenetically 37 basal insect Blattella germanica (L.) and to study their possible role in fluid 38 homeostasis during oogenesis. We isolated an ovarian AQP from B. germanica 39 (BgAQP) that has a deduced amino acid sequence showing six potential transmembrane 40 domains, two NPA motifs, and an ar/R constriction region, which are typical features of 41 the AQP family. Phylogenetic analyses indicated that BgAQP belongs to the PRIP 42 group of insect AQPs, previously suggested to be water-specific. However, ectopic 43 expression of BgAQP in Xenopus laevis (Daudin) oocytes demonstrated that this AQP 44 transports water and modest amounts of urea, but not glycerol, which suggests that 45 PRIP group of insect AQPs may have heterogeneous solute preferences. BgAQP was 46 shown to be highly expressed in the ovary, followed by the fat body and muscle tissues, 47 but water-stress did not modify significantly the ovarian expression levels. RNA 48 interference (RNAi) reduced BgAQP mRNA levels in the ovary but the oocytes 49 developed normally. The absence of an apparent ovarian phenotype after BgAQP RNAi 50 suggests that other functionally redundant AQPs that were not silenced in our 51 experiments might exist in the ovary of B. germanica.