The presence of water influences reproductive function in the song sparrow (Melospiza melodia morphna)

Cumulative evidence indicates that song sparrows, Melospiza melodia morphna, of western Washington State prefer territories close to water. Densities of territories were higher within 50m of open water and analysis of stomach contents revealed aquatic organisms. An unusually dry period (less open water) in May and June 1997 had no effect on latency of territorial males to respond to a simulated territorial intrusion (STI), but the number of songs and closest approach to the decoy were lower than those recorded in June 1988 (no major dry periods). A laboratory experiment was conducted in which males and females were exposed to long days to stimulate reproductive development. One group received a bath with water daily and the other group received a dry bath (both groups had ad libitum access to drinking water through a glass tube). Birds with a dry bath tended to show reduced photoperiodically-induced gonadal growth compared with birds that had access to water in the bath. Plasma levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) increased following photostimulation in all groups. However, LH levels were higher in females with access to water. There were no differences in hormone levels in any of the other groups. Taken together these novel data indicate that presence and access to open water could be an important environmental cue for song sparrows in western Washington State. Implications for global climate change and droughts are suggested.     

Structural insights into biased G protein-coupled receptor signaling revealed by fluorescence spectroscopy

G protein-coupled receptors (GPCRs) are seven-transmembrane proteins that mediate most cellular responses to hormones and neurotransmitters, representing the largest group of therapeutic targets. Recent studies show that some GPCRs signal through both G protein and arrestin pathways in a ligand-specific manner. Ligands that direct signaling through a specific pathway are known as biased ligands. The arginine-vasopressin type 2 receptor (V2R), a prototypical peptide-activated GPCR, is an ideal model system to investigate the structural basis of biased signaling. Although the native hormone arginine-vasopressin leads to activation of both the stimulatory G protein (Gs) for the adenylyl cyclase and arrestin pathways, synthetic ligands exhibit highly biased signaling through either Gs alone or arrestin alone. We used purified V2R stabilized in neutral amphipols and developed fluorescence-based assays to investigate the structural basis of biased signaling for the V2R. Our studies demonstrate that the Gs-biased agonist stabilizes a conformation that is distinct from that stabilized by the arrestin-biased agonists. This study provides unique insights into the structural mechanisms of GPCR activation by biased ligands that may be relevant to the design of pathway-biased drugs.