Morphogenesis of prechordal plate and notochord requires intact Eph/ephrin B signaling.

Eph receptors and their ligands, the ephrins, mediate cell-to-cell signals implicated in the regulation of cell migration processes during development. We report the molecular cloning and tissue distribution of zebrafish transmembrane ephrins that represent all known members of the mammalian class B ephrin family. The degree of homology among predicted ephrin B sequences suggests that, similar to their mammalian counterparts, zebrafish B-ephrins can also bind promiscuously to several Eph receptors. The dynamic expression patterns for each zebrafish B-ephrin support the idea that these ligands are confined to interact with their receptors at the borders of their complementary expression domains. Zebrafish B-ephrins are expressed as early as 30% epiboly and during gastrula stages: in the germ ring, shield, prechordal plate, and notochord. Ectopic overexpression of dominant-negative soluble ephrin B constructs yields reproducible defects in the morphology of the notochord and prechordal plate by the end of gastrulation. Notably disruption of Eph/ephrin B signaling does not completely destroy structures examined, suggesting that cell fate specification is not altered. Thus abnormal morphogenesis of the prechordal plate and the notochord is likely a consequence of a cell movement defect. Our observations suggest Eph/ephrin B signaling plays an essential role in regulating cell movements during gastrulation.

Note on the role of negative affectivity in understanding relationships between self-reports of exercise and sick leave.

Previous research indicates that observed correlations between self-reports of job stress and self-reports of strain may be reduced after partialling out the variance due to the personality trait of negative affectivity. The present study examined the effect of negative affectivity on the relationships between self-reports of exercise and strain in a sample of 128 governmental employees. While the magnitudes of the bivariate correlations between exercise and strain were small, the results of semipartial correlation analyses were somewhat consistent with expectations that the magnitudes of bivariate correlations between exercise participation and self-reports of strain would be reduced after controlling for negative affectivity in measures of strain. The implications of these findings for incorporating a measure of negative affectivity in studies of exercise-strain relationships involving self-reports are discussed.

Plasma membrane hyperpolarization effect on chromatin and protein biosynthesis in rat hepatocytes of different ages.

Plasmic membrane hyperpolarization resulted in a significant activation of the cell genome and a stimulation of the synthesis of total RNA and protein of hepatocytes. Changes in the level of membrane potential are thought to be one of the mechanisms of regulation of cell's genetic apparatus. In old age the stimulating effect of hyperpolarization is weakened that may be a cause of a change in protein biosynthesis.