Haem uptake is essential for egg production in the haematophagous blood fluke of humans, Schistosoma mansoni

Schistosomes ingest host erythrocytes, liberating large quantities of haem. Despite its toxicity, haem is an essential factor for numerous biological reactions, and may be an important iron source for these helminths. We used a fluorescence haem analogue, palladium mesoporphyrin, to investigate pathways of haem acquisition, and showed that palladium mesoporphyrin accumulates in the vitellaria (eggshell precursor glands) and ovary of female Schistosoma mansoni. Furthermore, incubation of adult females in 10-100 μm cyclosporin A (IC50 = 2.3 μm) inhibits the uptake of palladium mesoporphyrin to these tissues, with tenfold reductions in fluorescence intensity of the ovary. In vitro exposure to cyclosporin A resulted in significant perturbation of egg production, reducing egg output from 34 eggs per female to 5.7 eggs per female over the incubation period, and retardation of egg development. We characterized a S. mansoni homologue of the haem-responsive genes of Caenorhabditis elegans. The gene (Smhrg-1) encodes a protein with a molecular weight of approximately 17 kDa. SmHRG-1 was able to rescue growth in haem transport-deficient HEM1Δ yeast. Transcriptional suppression of Smhrg-1 in adult S. mansoni worms resulted in significant delay in egg maturation, with 47% of eggs from transcriptionally suppressed worms being identified as immature compared with only 27% of eggs laid by control worms treated with firefly luciferase. Our findings indicate the presence of transmembrane haem transporters in schistosomes, with a high abundance of these molecules being present in tissues involved in oogenesis.

Seasonal changes in broodstock spawning performance and egg quality in ballan wrasse (Labrus bergylta)

Sea lice continue to be one of the largest issues for the salmon farming industry and the use of ballan wrasse (Labrus bergylta) as a biological control is considered to be one of the most sustainable solutions in development. Broodstock management has proved challenging in the initial phases due to the significant lack of understanding of basic reproductive physiology and behaviour in the species. The aim of the study was to monitor captive breeding populations throughout a spawning season to examine timing and duration of spawning,quantify egg production, and look at seasonal changes in egg quality parameters as well as investigate the parental contribution to spawning events. A clear spawning rhythm was shown with 3-5 spawning periods inclusive of spawning windows lasting 1-9 days followed by inter spawning intervals of 8-12 days. Fertilization rate remained consistently high (> 87.5%) over the spawning season and did not differ significantly between spawning populations. Hatch rate was variable (0-97.5 %), but peaked in the middle of the spawning season. Meanoocyte diameter and gum layer thickness decreased slightly over the spawning season with no significant differences between spawning populations. Fatty acid (FA) profile of eggs remained consistent throughout the season and with the exception of high levels of ARA (3.8 ± 0.5 % of total FA) the FA profile was similar to that observed in other marine fish species. Parental contribution analysis showed 3 out of 6 spawning events to be single paired mating while the remaining 3 had contributions from multiple parents. Furthermore, the proposed multiple batch spawning nature of this species was confirmed with proof of a single femalecontributing to two separate spawning events. Overall this work represents the first comprehensive data set of spawning activity of captive ballan wrasse, and as such and will be helpful in formulating sustainable broodstock management plans for the species.

Suppression of the Insulin Receptors in Adult Schistosoma japonicum Impacts on Parasite Growth and Development: Further Evidence of Vaccine Potential

To further investigate the importance of insulin signaling in the growth, development, sexual maturation and egg production of adult schistosomes, we have focused attention on the insulin receptors (SjIRs) of Schistosoma japonicum, which we have previously cloned and partially characterised. We now show, by Biolayer Interferometry, that human insulin can bind the L1 subdomain (insulin binding domain) of recombinant (r)SjIR1 and rSjIR2 (designated SjLD1 and SjLD2) produced using the Drosophila S2 protein expression system. We have then used RNA interference (RNAi) to knock down the expression of the SjIRs in adult S. japonicum in vitro and show that, in addition to their reduced transcription, the transcript levels of other important downstream genes within the insulin pathway, associated with glucose metabolism and schistosome fecundity, were also impacted substantially. Further, a significant decrease in glucose uptake was observed in the SjIR-knockdown worms compared with luciferase controls. In vaccine/challenge experiments, we found that rSjLD1 and rSjLD2 depressed female growth, intestinal granuloma density and faecal egg production in S. japonicum in mice presented with a low dose challenge infection. These data re-emphasize the potential of the SjIRs as veterinary transmission blocking vaccine candidates against zoonotic schistosomiasis japonica in China and the Philippines.