Prostaglandins Do not Release Egg-Laying Behaviour in the Silkmoth, Bombyx mori

Roles of three putative salmon louse (Lepeophtheirus salmonis) prostaglandin E2 synthases in physiology and host-parasite interactions

BACKGROUND

The salmon louse (Lepeophtheirus salmonis) is a parasite of salmonid fish. Atlantic salmon (Salmo salar) exhibit only a limited and ineffective immune response when infested with this parasite. Prostaglandins (PGs) have many biological functions in both invertebrates and vertebrates, one of which is the regulation of immune responses. This has led to the suggestion that prostaglandin E₂ (PGE₂) is important in the salmon louse host-parasite interaction, although studies of a salmon louse prostaglandin E₂ synthase (PGES) 2 gene have not enabled conformation of this hypothesis. The aim of the present study was, therefore, to characterize two additional PGES-like genes.

METHODS

Lepeophtheirus salmonis microsomal glutathione S-transferase 1 like (LsMGST1L) and LsPGES3L were investigated by sequencing, phylogenetics, transcript localization and expression studies. Moreover, the function of these putative PGES genes in addition to the previously identified LsPGES2 gene was analyzed in double stranded (ds) RNA-mediated knockdown (KD) salmon louse.

RESULTS

Analysis of the three putative LsPGES genes showed a rather constitutive transcript level throughout development from nauplius to the adult stages, and in a range of tissues, with the highest levels in the ovaries or gut. DsRNA-mediated KD of these transcripts did not produce any characteristic changes in phenotype, and KD animals displayed a normal reproductive output. The ability of the parasite to infect or modulate the immune response of the host fish was also not affected by KD.

CONCLUSIONS

Salmon louse prostaglandins may play endogenous roles in the management of reproduction and oxidative stress and may be a product of salmon louse blood digestions.

Presence of eupyrene spermatozoa in vestibulum accelerates oviposition in the silkworm moth, Bombyx mori

In the silkmoth, Bombyx mori, mating accelerates egg laying. Sterilized males did not induce females to oviposit, whereas artificial insemination was enough to accelerate oviposition. These findings showed that mechanical stimulation of the outer reproductive organs and the bursa copulatrix (BC) had no effect on oviposition. Factors included in seminal fluids also did not stimulate oviposition because neither implantation of female internal reproductive organs nor injection of the spermatophore extract into virgin females activated oviposition. Preventing sperm precedence by experimental removal of the BC or spermatheca inhibited activation of egg laying. More precise surgeries on the spermatheca showed that the main factor for eliciting oviposition was the presence of matured and fertile eupyrene spermatozoa in the vestibulum. Sperm were not effective unless they reached the vestibulum. Nerve transection and electrophysiological studies revealed that nerve 4 of the terminal abdominal ganglion was the pathway by which the mating signal was transmitted toward the higher central nervous system.