Prenylation is essential for the enrichment of cone phosphodiesterase-6 (PDE6) in outer segments and efficient cone phototransduction

Phosphodiesterase-6 (PDE6) is the key phototransduction effector enzyme residing in the outer segment (OS) of photoreceptors. Cone PDE6 is a tetrameric protein consisting of two inhibitory subunits (γ') and two catalytic subunits (α'). The catalytic subunit of cone PDE6 contains a C-terminus prenylation motif. Deletion of PDE6α' C-terminal prenylation motif is linked to achromatopsia (ACHM), a type of color blindness in humans. However, mechanisms behind the disease and roles for lipidation of cone PDE6 in vision are unknown. In this study, we generated two knock-in mouse models expressing mutant variants of cone PDE6α' lacking the prenylation motif (PDE6α'∆C). We find that the C-terminal prenylation motif is the primary determinant for the association of cone PDE6 protein with membranes. Cones from PDE6α'∆C homozygous mice are less sensitive to light, and their response to light is delayed, whereas cone function in heterozygous PDE6α'∆C/+ mice is unaffected. Surprisingly, the expression level and assembly of cone PDE6 protein were unaltered in the absence of prenylation. Unprenylated assembled cone PDE6 in PDE6α'∆C homozygous animals is mislocalized and enriched in the cone inner segment and synaptic terminal. Interestingly, the disk density and the overall length of cone OS in PDE6α'∆C homozygous mutants are altered, highlighting a novel structural role for PDE6 in maintaining cone OS length and morphology. The survival of cones in the ACHM model generated in this study bodes well for gene therapy as a treatment option for restoring vision in patients with similar mutations in the PDE6C gene.

Rapid and socially induced change of a badge of status

This paper reports a new aspect of male signalling in the green swordtail Xiphophorus hellerii. Males are highly ornamented and possess a sword (an extension of the caudal fin), as well as a lateral stripe that has been shown to be a badge of status. Males of one natural population, however, were found to quickly change the colour of their lateral stripe to red when socially dominant over other males and black when subdominant, thereby exploiting the female preference for red stripes while dominant, and avoiding the costs of male aggression while subdominant.

Can recovering alcoholics help hospitalized patients with alcohol problems?

OBJECTIVE

The researchers evaluated the relative effectiveness of 2 interventions for patients with alcohol problems.

STUDY DESIGN

A nonrandomized intervention study was used to compare usual care (control) with a 5- to 15-minute physician-delivered message (brief intervention) and with the physician message plus a 30- to 60-minute visit by a recovering alcoholic (peer intervention). Telephone follow-up was obtained up to 12 months after hospital discharge that focused on patient behaviors during the first 6 months following discharge.

POPULATION

The study included 314 patients with alcohol-related injuries admitted to an urban teaching hospital.

OUTCOMES MEASURED

Researchers measured complete abstinence from alcohol during the entire 6 months following hospital discharge, abstinence from alcohol during the sixth month following hospital discharge, and initiation of alcohol treatment or self-help within 6 months of hospital discharge.

RESULTS

Valid responses were obtained from 140 patients (45%). Observed success rates were: 34%, 44%, and 59% (P=.012) for abstinence from alcohol since discharge in the usual care group, the brief intervention group, and the peer intervention group, respectively; 36%, 51%, and 64% (P=.006) for abstinence at the sixth month following hospital discharge; and 9%, 15%, and 49% (P &it.001) for initiation of treatment/self-help. During the telephone follow-up interview, several patients in the peer intervention group expressed gratitude for the help they received with their drinking problems while in the hospital. A few patients dramatically changed their lives. They went from being unemployed and homeless to full-time employment and having a permanent residence. They credited the peer intervention as being the most important factor that motivated them to seek help for their alcohol use disorder. One of these individuals serves as a volunteer, visiting hospitalized patients with drinking problems.

CONCLUSIONS

Among trauma victims with injuries severe enough to require hospital admission, brief advice from a physician followed by a visit with a recovering alcoholic appears to be an effective intervention. Although further study is needed to confirm these findings, in the meantime physicians can request that members of Alcoholics Anonymous (AA) visit their hospitalized patients who have alcohol use disorders. Interventions by recovering alcoholics are part of their twelfth-step work (an essential part of the AA program) and are simple, practical, involve no costs, and pose little patient risk. They can be arranged from the patient's bedside telephone. Some patients will show a dramatic response to these peer visits.

The effects of iodination on the receptor binding affinity of ovine prolactin

A completely iodinated form of ovine prolactin was prepared using lactoperoxidase. The iodination was characterized using gel filtration, electrophoresis and fluorescence analysis. Complete iodination corresponds to a 33% decrease in intrinsic tryptophanyl fluorescence (275 parallel 348). Each ovine prolactin molecule possesses four iodination sites which cannot be distinguished by kinetic analysis. The receptor binding capacity of the tetraiodoprolactin was also assayed using the particulate fraction from female rat livers. Although the total binding capacity of native and iodoprolactins is indistinguishable, significant differences in receptor binding behavior were observed.