A novel terpene synthase controls differences in anti-aphrodisiac pheromone production between closely related Heliconius butterflies

Plants and insects often use the same compounds for chemical communication, but not much is known about the genetics of convergent evolution of chemical signals. The terpene (E)-β-ocimene is a common component of floral scent and is also used by the butterfly Heliconius melpomene as an anti-aphrodisiac pheromone. While the biosynthesis of terpenes has been described in plants and microorganisms, few terpene synthases (TPSs) have been identified in insects. Here, we study the recent divergence of 2 species, H. melpomene and Heliconius cydno, which differ in the presence of (E)-β-ocimene; combining linkage mapping, gene expression, and functional analyses, we identify 2 novel TPSs. Furthermore, we demonstrate that one, HmelOS, is able to synthesise (E)-β-ocimene in vitro. We find no evidence for TPS activity in HcydOS (HmelOS ortholog of H. cydno), suggesting that the loss of (E)-β-ocimene in this species is the result of coding, not regulatory, differences. The TPS enzymes we discovered are unrelated to previously described plant and insect TPSs, demonstrating that chemical convergence has independent evolutionary origins.

Plants and insects often use the same compounds for chemical communication, but little is known about the convergent evolution of such chemical signals. This study identifies a novel terpene synthase involved in production of an anti-aphrodisiac pheromone by the butterfly Heliconius melpomene. This enzyme is unrelated to other insect terpene synthases, providing evidence that the ability to synthesise terpenes has arisen multiple times independently within the insects.     

Use of qPCR-Based Cercariometry to Assess Swimmer’s Itch in Recreational Lakes

Swimmer’s itch (cercarial dermatitis) is a nuisance encountered by bathers and recreational water users worldwide. The condition is caused by the penetration of larval digenean trematodes (cercariae) of the family Schistosomatidae, into the skin, following their release into freshwater from pulmonate snails that serve as the intermediate hosts for these parasites. This study utilizes qPCR-based cercariometry to monitor and quantify cercariae from water samples collected at 5 lakes in northern Michigan. The resolution provided by qPCR facilitated assessment of the environmental and biological drivers of swimmer’s itch-causing cercariae concentrations, allowing us to demonstrate that cercarial abundance is greatest at the top of the water column, in locations with prevailing on- and alongshore winds.     

Endothelin-1 release from lamb ductus arteriosus: relevance to postnatal closure of the vessel

Our previous investigations have shown that endothelin-1 (ET-1) is a singularly potent constrictor of the ductus arteriosus and that a cytochrome P-450 system located in the sarcolemma is crucial for the contractile response of the vessel to oxygen. We have now studied the release of ET-1 from isolated ductus arteriosus preparations of near-term fetal lambs. Preparations produced measurable amounts of ET-1 under basal conditions (about 0.04 pg/100 mg wet weight.min) both in the presence and absence of the endothelium. Anisomycin (10(-4) M) reduced this release by 50%, while thrombin (1 U/mL) doubled the release. Treatment with a CO mixture (CO/O2 ratio, 0.27) inhibited ET-1 release from intact and endothelium-denuded preparations. We propose that oxygen triggers closure of the ductus arteriosus at birth by causing a conformational change in a specific cytochrome P-450, which, in turn, provides the signal for the synthesis of the constrictor ET-1.     

Human lymphocytes exposed to low doses of X-rays are less susceptible to radiation-induced mutagenesis

Human lymphocytes exposed to low doses of X-rays become refractory to the subsequent induction of chromosomal damage by high doses of radiation (Shadley and Wolff, 1987). The current study was designed to test the effect of pretreatment of human T-lymphocytes with a low dose of X-rays on the induction of mutations at the hprt locus by a subsequent challenge dose. When cells were exposed to 1 cGy X-rays 24 h after phytohemagglutinin stimulation, the yield of mutations induced by a 300 cGy X-ray dose given 16 h later was reduced by approximately 70% from the control level of X-ray-induced mutations. This indicates that this previously described adaptive response to low dose X-rays also results in lymphocytes becoming refractory to the induction of gene mutations.