Enhanced myogenesis in NCAM-transfected mouse myoblasts

The fusion of mononucleate precursor myoblasts to form the multinucleated skeletal muscle fibre is proceeded by a series of complex cell-cell interactions but the cell-surface molecules involved in these events have not been characterized. During myogenesis in vivo and in vitro, expression of the neural cell adhesion molecule (NCAM) undergoes an isoform transition that precisely correlates with terminal myoblast differentiation and myotube formation. Altered processing of RNA results in the replacement of the transmembrane NCAM (relative molecular mass, 145,000 (145K) in proliferating myoblasts by a predominant 125K NCAM form linked to glycosyl phosphatidylinositol in myotubes. We now report that mouse myoblasts transfected to constitutively express the human muscle-specific 125K glycosylphosphatidylinositol-linked NCAM isoform more readily fuse to form myotubes. This suggests that NCAM plays a part in myoblast fusion and that the isoform switch may promote this function.     

A receptor that mediates the post-mating switch in Drosophila reproductive behaviour

Mating in many species induces a dramatic switch in female reproductive behaviour. In most insects, this switch is triggered by factors present in the male's seminal fluid. How these factors exert such profound effects in females is unknown. Here we identify a receptor for the Drosophila melanogaster sex peptide (SP, also known as Acp70A), the primary trigger of post-mating responses in this species. Females that lack the sex peptide receptor (SPR, also known as CG16752), either entirely or only in the nervous system, fail to respond to SP and continue to show virgin behaviours even after mating. SPR is expressed in the female's reproductive tract and central nervous system. The behavioural functions of SPR map to the subset of neurons that also express the fruitless gene, a key determinant of sex-specific reproductive behaviour. SPR is highly conserved across insects, opening up the prospect of new strategies to control the reproductive and host-seeking behaviours of agricultural pests and human disease vectors.     

A single class of olfactory neurons mediates behavioural responses to a Drosophila sex pheromone

Insects, like many other animals, use sex pheromones to coordinate their reproductive behaviours. Volatile pheromones are detected by odorant receptors expressed in olfactory receptor neurons (ORNs). Whereas fruit odours typically activate multiple ORN classes, pheromones are thought to act through single dedicated classes of ORN. This model predicts that activation of such an ORN class should be sufficient to trigger the appropriate behavioural response. Here we show that the Drosophila melanogaster male-specific pheromone 11-cis-vaccenyl acetate (cVA) acts through the receptor Or67d to regulate both male and female mating behaviour. Mutant males that lack Or67d inappropriately court other males, whereas mutant females are less receptive to courting males. These data suggest that cVA has opposite effects in the two sexes: inhibiting mating behaviour in males but promoting mating behaviour in females. Replacing Or67d with moth pheromone receptors renders these ORNs sensitive to the corresponding moth pheromones. In such flies, moth pheromones elicit behavioural responses that mimic the normal response to cVA. Thus, activation of a single ORN class is both necessary and sufficient to mediate behavioural responses to the Drosophila sex pheromone cVA.     

The genomic basis of adaptive evolution in threespine sticklebacks

Marine stickleback fish have colonized and adapted to thousands of streams and lakes formed since the last ice age, providing an exceptional opportunity to characterize genomic mechanisms underlying repeated ecological adaptation in nature. Here we develop a high-quality reference genome assembly for threespine sticklebacks. By sequencing the genomes of twenty additional individuals from a global set of marine and freshwater populations, we identify a genome-wide set of loci that are consistently associated with marine-freshwater divergence. Our results indicate that reuse of globally shared standing genetic variation, including chromosomal inversions, has an important role in repeated evolution of distinct marine and freshwater sticklebacks, and in the maintenance of divergent ecotypes during early stages of reproductive isolation. Both coding and regulatory changes occur in the set of loci underlying marine-freshwater evolution, but regulatory changes appear to predominate in this well known example of repeated adaptive evolution in nature.     

Cline stripped of research grants

The National Institutes of Health (NIH) decided earlier this year to require special prior approval for all future grant requests from Dr. Martin Cline, of the University of California at Los Angeles, because of his unauthorized experiments on human patients involving the use of recombinant DNA techniques. The National Heart, Lung and Blood Institute, one of three NIH institutes funding research by Cline, has now taken the further step of prematurely terminating its current grant to Cline.