Osiris17 is indispensable for morphogenesis of intestinal tract in Locusta migratoria.

The Osiris gene family is believed to play important roles in insect biology. Previous studies mainly focused on the roles of Osiris in Drorophila, how Osiris operates during the development of other species remains largely unknown. Here, we investigated the role of LmOsi17 in development of the hemimetabolous insect Locusta migratoria. LmOsi17 was highly expressed in the intestinal tract of nymphs. Knockdown of LmOsi17 by RNA interference (RNAi) in nymphs resulted in growth defects. The dsLmOsi17-injected nymphs did not increase in body weight or size and eventually died. Immunohistochemical analysis showed that LmOsi17 was localized to the epithelial cells of the foregut and the gastric caecum. Histological observation and hematoxylin-eosin staining indicate that the foregut and gastric caecum are deformed in dsLmOsi17 treated nymphs, suggesting that LmOsi17 is involved in morphogenesis of foregut and gastric caecum. In addition, we observed a significant reduction in the thickness of the new cuticle in dsLmOsi17-injected nymphs compared to control nymphs. Taken together, these results suggest that LmOsi17 contributes to morphogenesis of intestinal tract that affects growth and development of nymphs in locusts.

The larval midgut of Anopheles, Aedes, and Toxorhynchites mosquitoes (Diptera, Culicidae): a comparative approach in morphophysiology and evolution.

The mosquito larval midgut is responsible for acquiring and storing most of the nutrients that will sustain the events of metamorphosis and the insect's adult life. Despite its importance, the basic biology of this larval organ is poorly understood. To help fill this gap, we carried out a comparative morphophysiological investigation of three larval midgut regions (gastric caeca, anterior midgut, and posterior midgut) of phylogenetically distant mosquitoes: Anopheles gambiae (Anopheles albimanus was occasionally used as an alternate), Aedes aegypti, and Toxorhynchites theobaldi. Larvae of Toxorhynchites mosquitoes are predacious, in contrast to the other two species, that are detritivorous. In this work, we show that the larval gut of the three species shares basic histological characteristics, but differ in other aspects. The lipid and carbohydrate metabolism of the An. gambiae larval midgut is different compared with that of Ae. aegypti and Tx. theobaldi. The gastric caecum is the most variable region, with differences probably related to the chemical composition of the diet. The peritrophic matrix is morphologically similar in the three species, and processes involved in the post-embryonic development of the organ, such as cell differentiation and proliferation, were also similar. FMRF-positive enteroendocrine cells are grouped in the posterior midgut of Tx. theobaldi, but individualized in An. gambiae and Ae. aegypti. We hypothesize that Tx. theobaldi larval predation is an ancestral condition in mosquito evolution.

Effects of rearing salinity on expression and function of ion-motive ATPases and ion transport across the gastric caecum of Aedes aegypti larvae.

Larvae of Aedes aegypti, the yellow fever vector, inhabit a variety of aquatic habitats ranging from freshwater to brackish water. This study focuses on the gastric caecum of the larvae, an organ that has not been widely studied. We provide the first measurements of H+, K+ and Na+ fluxes at the distal and proximal gastric caecum, and have shown that they differ in the two regions, consistent with previously reported regionalization of ion transporters. Moreover, we have shown that the regionalization of vacuolar H+-ATPase and Na+/K+-ATPase is altered when larvae are reared in brackish water (30% seawater) relative to freshwater. Measurements of luminal Na+ and K+ concentrations also show a 5-fold increase in Na+/K+ ratio in the caecal lumen in larvae reared in brackish water relative to freshwater, whereas transepithelial potential and luminal pH were unchanged. Calculated electrochemical potentials reveal changes in the active accumulation of Na+ and K+ in the lumen of the gastric caecum of freshwater versus brackish water larvae. Together with the results of previous studies of the larval midgut, our results show that the caecum is functionally distinct from the adjacent anterior midgut, and may play an important role in osmoregulation as well as uptake of nutrients.

Ultrastructural comparison of the larval midguts between Trypoxylus dichotomus (Linnaeus, 1771) and Anomala corpulenta (Motschulsky, 1854) (Coleoptera: Scarabaeidae).

Larvae are the most important feeding and developmental stage in the life cycle of insects. Correspondingly, the larval midguts, as the primary digestive organs, undergo diverse specialization among insect lineages. Larvae of Scarabaeoidae, commomly known as white grubs, exhibit diversity on feeding habits at the familial or subfamilial level. However, the ultrastructure of larval midguts is not yet satisfactorily understood. In this study, the larval midguts of Trypoxylus dichotomus and Anomala corpulenta were compared using light and transmission electron microscopy for the first time, to uncover the ultrastructural differences between the midguts of saprophagous and phytophagous white grubs. The larval midguts of both species are tubular with three circles of the gastric caeca, and share morphological similarities in midgut epithelial cells, layers of basal lamina, and the digestive and regenerative cells. However, the midguts of the two species differ significantly in the shape of the gastric caeca and exhibit slightly differences in muscle structure. The morphology of larval midgut is related to the feeding habits.

Mechanisms of transport of H+, Na+ and K+, across the distal gastric caecum of larval Aedes aegypti.

Measured changes in ion fluxes, transepithelial potential (TEP) and basolateral membrane potential (Vb) in response to ion transporter inhibitors were used to assess the mechanisms of transport of H+, Na+ and K+, across the distal gastric caecum of larval Aedes aegypti, a vector of yellow fever. Preparations were stimulated with 5-hydroxytryptamine (5-HT, 10-6 M) in order to maintain stable rates of H+, Na+, and K+ transport across the distal caecum. Transepithelial potential (TEP), basolateral membrane potential (Vb), and H+, Na+ and K+ fluxes all declined after the addition of a vacuolar-type H+-ATPase (VA) inhibitor, n-ethlymaleimide (NEM), consistent with a primary role for VA in energizing ion transport across the distal gastric caecum. Amiloride also inhibited H+, Na+, and K+ fluxes, consistent with an apically expressed VA that is coupled to a cation:H+ antiporter (AeNHE8), analogous to the coupling of apical VA and cation:nH+ antiporter in Malpighian tubules. A working model of transport of H+, Na+ and K+ across the distal gastric caecum proposes that coupling of VA and AeNHE8 in the apical membrane leads to the removal of intracellular Na+ or K+, thus creating favourable ion gradients to promote the activity of two transporters in the basal membrane, cation:H+ antiporter (AeNHE3) and a bumetanide-sensitive cation chloride cotransporter (CCC).