Cut‐points for Waist Circumference in Europids and South Asians

There is little strong evidence that currently recommended higher waist circumference cut‐points for Europids compared with South Asians are associated with similar risk for type 2 diabetes. This study was designed to provide such evidence. Longitudinal studies over 5 years were conducted among 5,515 Europid and 2,214 ethnically South Asian participants. Age‐standardized diabetes incidence at different levels of waist circumference and incidence difference relative to a reference value were calculated. The Youden Index was used to determine waist circumference cut‐points. At currently recommended cut‐points, estimated annual diabetes incidence for a 50‐year‐old Europid was <0.6% for both sexes, and for a 50‐year‐old South Asian, 5.8% for men and 2.1% for women. Annual diabetes incidence of 1% was observed for a 50 year old at a waist circumference 35–40 cm greater in Europid compared to South Asian men and women. Incidence difference between recommended cut‐points and a reference value (80 cm in men, 70 cm in women) was 0.3 and 4.4% per year for Europid and South Asian men, and 0.2 and 0.8% per year for Europid and South Asian women, respectively. Waist circumference cut‐points chosen using the Youden Index were shown to be dependent on obesity levels in the population. The much higher observed risk of diabetes in South Asians compared to Europids at the respective recommended waist circumference cut‐points suggests that differences between them should be greater. Approaches that use the Youden Index to select waist circumference cut‐points are inappropriate and should not be used for this purpose.     

Analysis of Ca2+ mediated signaling regulating Toxoplasma infectivity reveals complex relationships between key molecules

Host cell invasion, exit and parasite dissemination is critical to the pathogenesis of apicomplexan parasites such as Toxoplasma gondii and Plasmodium spp. These processes are regulated by intracellular Ca²⁺ signaling although the temporal dynamics of Ca²⁺ fluxes and down‐stream second messenger pathways are poorly understood. Here, we use a genetically encoded biosensor, GFP‐Calmodulin‐M13–6 (GCaMP6), to capture Ca²⁺ flux in live Toxoplasma and investigate the role of Ca²⁺ signaling in egress and motility. Our analysis determines how environmental cues and signal activation influence intracellular Ca²⁺ flux, allowing placement of effector molecules within this pathway. Importantly, we have identified key interrelationships between cGMP and Ca²⁺ signaling that are required for activation of egress and motility. Furthermore, we extend this analysis to show that the Ca²⁺ Dependent Protein Kinases–TgCDPK1 and TgCDPK3—play a role in signal quenching before egress. This work highlights the interrelationships of second messenger pathways of Toxoplasma in space and time, which is likely required for pathogenesis of all apicomplexan species.     

The Inner Membrane Complex Sub-compartment Proteins Critical for Replication of the Apicomplexan Parasite Toxoplasma gondii Adopt a Pleckstrin Homology Fold

Toxoplasma gondii, an apicomplexan parasite prevalent in developed nations, infects up to one-third of the human population. The success of this parasite depends on several unique structures including an inner membrane complex (IMC) that lines the interior of the plasma membrane and contains proteins important for gliding motility and replication. Of these proteins, the IMC sub-compartment proteins (ISPs) have recently been shown to play a role in asexual T. gondii daughter cell formation, yet the mechanism is unknown. Complicating mechanistic characterization of the ISPs is a lack of sequence identity with proteins of known structure or function. In support of elucidating the function of ISPs, we first determined the crystal structures of representative members TgISP1 and TgISP3 to a resolution of 2.10 and 2.32 Å, respectively. Structural analysis revealed that both ISPs adopt a pleckstrin homology fold often associated with phospholipid binding or protein-protein interactions. Substitution of basic for hydrophobic residues in the region that overlays with phospholipid binding in related pleckstrin homology domains, however, suggests that ISPs do not retain phospholipid binding activity. Consistent with this observation, biochemical assays revealed no phospholipid binding activity. Interestingly, mapping of conserved surface residues combined with crystal packing analysis indicates that TgISPs have functionally repurposed the phospholipid-binding site likely to coordinate protein partners. Recruitment of larger protein complexes may also be aided through avidity-enhanced interactions resulting from multimerization of the ISPs. Overall, we propose a model where TgISPs recruit protein partners to the IMC to ensure correct progression of daughter cell formation.     

Ontogeny of feeding in two native and one alien fish species from the Murray-Darling Basin, Australia

Investigations into the feeding of the early stages of fishes can provide insights into processes influencing recruitment. In this study, we examined ontogenetic changes in morphology and feeding behaviour of two native Australian freshwater species, Murray cod, Maccullochella peelii peelii, and golden perch, Macquaria ambigua, and the alien species, common carp, Cyprinus carpio. Murray cod free embryos are large and well developed at the onset of feeding, whereas the other two species begin exogenous feeding much younger and are smaller and less-developed. Carp commence exogenous feeding 3 days earlier than golden perch, and show more advanced development of the eyes and ingestive apparatus. We conducted feeding experiments, presenting larvae of the three species with a standardised prey mix (comprising equal numbers of small calanoid copepods, large calanoid copepods, small Daphnia, and large Daphnia). Larvae of most tested ages and species showed a preference for mid-sized prey (300–500 μm wide). This was true even when their gapes substantially exceeded the largest prey offered. Daphnia were consumed more than similar-sized copepods. The results of this study suggest that survival through their larval period will be threatened in all three species if catchable prey <500 μm in width are not available throughout such time. They also suggest that interspecific competition for prey may occur, especially when larvae are very young. The precocious development of structures involved in feeding and the extended transition from endogenous to exogenous feeding of early carp larvae are likely to have contributed to the success of this species since its introduction to Australia.