Genomic content of chemosensory receptors in two sister blister beetles facilitates characterization of chemosensory evolution.

BACKGROUND: More than 2500 species belong to the Meloidae family (Coleoptera: Tenebrionoidea), members of which produce the potent defensive blistering agent cantharidin and are commonly known as blister beetles or Spanishflies. Cantharidin has recently been used for cancer therapy. Hycleus cichorii and Hycleus phaleratus have been used in traditional Chinese medicine for more than 2000 years due to their ability to biosynthesize cantharidin. To understand the role of the chemosensory system in beetle evolution, we comparatively analysed the chemosensory receptor families of both blister beetle species and compared them with those of other beetles. RESULTS: We identified 89 odorant receptors (ORs), 86 gustatory receptors (GRs), and 45 ionotropic receptors (IRs) in H. phaleratus and 149 ORs, 102 GRs and 50 IRs in H. cichorii. Nine groups of beetle ORs were recovered, and a similar pattern of ORs in Coleoptera emerged. Two evident expanded clades in Hycleus (Groups 5A and 3) were reconstructed in the phylogenetic tree. Four of eight genes with evidence of positive selection were clustered in the expanded clades of Group 5A. Three, eight and three orthologous pairs of CO2, sugar and fructose receptors, respectively, were identified in both blister beetles. Two evident expanded clades of putative bitter GRs in Hycleus were also found, and the GR in one clade had notably low divergence. Interestingly, IR41a was specifically expanded in blister beetles compared to other insects identified to date, and IR75 was also clearly expanded in both blister beetles based on our phylogenetic tree analysis. Moreover, evidence of positive selection was detected for eight ORs, three GRs and two IRs, half of which were from five duplicate clades. CONCLUSIONS: We first annotated the chemosensory receptor families in a pair of sister beetle genomes (Meloidae: Hycleus), which facilitated evolutionary analysis of chemosensory receptors between sibling species in the Coleoptera group. Our analysis suggests that changes in chemosensory receptors have a possible role in chemical-based species evolution in blister beetles. Future studies should include more species to verify this correlation, which will help us understand the evolution of blister beetles.

The BBSome in POMC and AgRP Neurons Is Necessary for Body Weight Regulation and Sorting of Metabolic Receptors.

The BBSome, a complex of eight Bardet-Biedl syndrome (BBS) proteins involved in cilia function, has emerged as an important regulator of energy balance, but the underlying cellular and molecular mechanisms are not fully understood. Here, we show that the control of energy homeostasis by the anorexigenic proopiomelanocortin (POMC) neurons and orexigenic agouti-related peptide (AgRP) neurons require intact BBSome. Targeted disruption of the BBSome by Bbs1 gene deletion in POMC or AgRP neurons increases body weight and adiposity. We demonstrate that obesity in mice lacking the Bbs1 gene in POMC neurons is associated with hyperphagia. Mechanistically, we present evidence implicating the BBSome in the trafficking of G protein-coupled neuropeptide Y Y2 receptor (NPY2R) and serotonin 5-hydroxytryptamine (HT)2C receptor (5-HT2CR) to cilia and plasma membrane, respectively. Consistent with this, loss of the BBSome reduced cell surface expression of the 5-HT2CR, interfered with serotonin-evoked increase in intracellular calcium and membrane potential, and blunted the anorectic and weight-reducing responses evoked by the 5-HT2cR agonist, lorcaserin. Finally, we show that disruption of the BBSome causes the 5-HT2CR to be stalled in the late endosome. Our results demonstrate the significance of the hypothalamic BBSome for the control of energy balance through regulation of trafficking of important metabolic receptors.

Vigabatrin induces tonic inhibition via GABA transporter reversal without increasing vesicular GABA release.

Two forms of GABAergic inhibition coexist: fast synaptic neurotransmission and tonic activation of GABA receptors due to ambient GABA. The mechanisms regulating ambient GABA have not been well defined. Here we examined the role of the GABA transporter in the increase in ambient [GABA] induced by the anticonvulsant vigabatrin. Pretreatment of cultured rat hippocampal neurons with vigabatrin (100 microM) for 2-5 days led to a large increase in ambient [GABA] that was measured as the change in holding current induced by bicuculline during patch-clamp recordings. In contrast, there was a decrease in the frequency of spontaneous miniature inhibitory postsynaptic currents mIPSCs with no change in their amplitude distribution, and a decrease in the magnitude of IPSCs evoked by presynaptic stimulation during paired recordings. The increase in ambient [GABA] was not prevented by blockade of vesicular GABA release with tetanus toxin or removal of extracellular calcium. During perforated patch recordings, the increase in ambient [GABA] was prevented by blocking the GABA transporter, indicating that the GABA transporter was continuously operating in reverse and releasing GABA. In contrast, blocking the GABA transporter increased ambient [GABA] during whole cell patch-clamp recordings unless GABA and Na(+) were added to the recording electrode solution, indicating that whole cell recordings can lead to erroneous conclusions about the role of the GABA transporter in control of ambient GABA. We conclude that the equilibrium for the GABA transporter is a major determinant of ambient [GABA] and tonic GABAergic inhibition. We propose that fast GABAergic neurotransmission and tonic inhibition can be independently modified and play complementary roles in control of neuronal excitability.