Larval diapause termination in the bamboo borer, Omphisa fuscidentalis

Expression of aquaporin and Na+/K+-ATPase in gill and gut cells of the shrimp Palaemon argentinus regulated by ecdysone

The crustacean molting cycle is triggered by the elevation of ecdysteroid levels in the hemolymph during late pre-molt. It is known that these animals absorb water through the intestine and gills to promote bodily swelling and rupture of the old exoskeleton. The participation of two membrane proteins responsible for the most uptake of water during the late pre-molt has been shown in the gill and gut cells of the freshwater shrimp Palaemon argentinus: Na+/K+-ATPase (NKA), which generates an osmoionic gradient, and Aquaporins (AQPs), water channels, which provide higher water permeability. Studies investigating the action of ecdysteroids on these proteins are scarce. Therefore, we investigated 20-hydroxyecdisone (20E) in relation to the regulation of NKA and AQPs in the gill and gut cells of P. argentinus. We exposed primary cultures of both gut and gill cells to 20E. Gill cells treated with hormone in the presence of NKA-blockers, exhibited a reduction in volume, and cells treated with 20E showed a greater expression of NKA than untreated cells. Additionally, gills cells treated with 20E showed an increase in volume (∼60%), which the aquaporin inhibitor (HgCl2) prevented. The participation of AQPs in the influx of water was corroborated by a greater expression of AQP in cells treated with 20E compared to untreated cells. Gut cells of animals in intermolt exposed to hormone (20E) maintained their initial cell volume. With the addition of HgCl2, these cells showed a reduction in volume similar to cells of animals in pre-molt. Immunocytochemistry showed a high expression of AQP in gut cells treated with 20E. These findings suggest that 20E regulates the expression of AQP and NKA in the late pre-molt, to provide water uptake for molting. This work offers new perspectives concerning the molting hormone, placing it as a crucial part of water uptake for ecdysis.

Diapause hormone directly stimulates the prothoracic glands of diapause larvae under juvenile hormone regulation in the bamboo borer, Omphisa fuscidentalis Hampson

Larval diapause in many lepidopteran insects is induced and maintained by high juvenile hormone (JH). In the case of the bamboo borer, Omphisa fuscidentalis, the effect of JH is the opposite: The application of juvenile hormone analog (JHA: S-methoprene) terminates larval diapause, unlike in other insect species. Here, we analyzed the expression of JH-receptor Met, DH-PBAN, and Kr-h1 in the subesophageal ganglion (SG) from October to April using semi-quantitative polymerase chain reaction (PCR). The results show that OfMet and OfDH-PBAN messenger RNA in the SG are mainly expressed during the larval diapause stage, while OfKr-h1 increases during the pupal stage. Using tissue culture techniques and an enzyme-linked immunosorbent assay (ELISA), diapause hormone (DH) was found to induce ecdysteroidogenesis in the culture medium of the prothoracic gland (PG) after incubation for 30 min with 25 ng and 50 ng of DH. Thus, DH is a novel stimulator for the PG. We identified a DHR homolog in the bamboo borer and confirmed that it is expressed in the PG. In addition, for in vitro experiments, DH increased the expression levels of OfDHR, OfEcR-A, and ecdysone-inducible genes in the PG. These results demonstrate that DH can function as a prothoracicotropic factor, and this function of DH might be through of DHR expressed on PG cells. Consequently, DH is one of the key factors in larval diapause break which is triggered by JH in the bamboo borer, O. fuscidentalis.