Spectral densities of nitrogen nuclei in Escherichia coli ribonuclease HI obtained by 15N NMR relaxation and molecular dynamics

Summary Spectral densities of the ¹⁵N amide in Escherichia coli ribonuclease HI, obtained from NMR relaxation experiments, were compared with those calculated using a molecular dynamics (MD) simulation. All calculations and comparisons assumed that the auto-correlation function describing the internal motions of the molecule was independent of the auto-correlation function associated with overall rotational diffusion. Comparisons were limited to those residues for which the auto-correlation function of internal motions rapidly relaxed and reached a steady state within 205 ps. The results show the importance of frequency components as well as amplitudes of internal motions in order to obtain a meaningful comparison of MD simulations with NMR data.     

LIN-41 inactivation leads to delayed centrosome elimination and abnormal chromosome behavior during female meiosis in Caenorhabditis elegans

During oogenesis, two successive meiotic cell divisions occur without functional centrosomes because of the inactivation and subsequent elimination of maternal centrosomes during the diplotene stage of meiosis I. Despite being a conserved phenomenon in most metazoans, the means by which this centrosome behavior is controlled during female meiosis remain elusive. Here, we conducted a targeted RNAi screening in the Caenorhabditis elegans gonad to identify novel regulators of centrosome behavior during oogenesis. We screened 513 genes known to be essential for embryo production and directly visualized GFP–γ-tubulin to monitor centrosome behavior at all stages of oogenesis. In the screening, we found that RNAi-mediated inactivation of 33 genes delayed the elimination of GFP–γ-tubulin at centrosomes during oogenesis, whereas inactivation of nine genes accelerated the process. Depletion of the TRIM-NHL protein LIN-41 led to a significant delay in centrosome elimination and to the separation and reactivation of centrosomes during oogenesis. Upon LIN-41 depletion, meiotic chromosomes were abnormally condensed and pulled toward one of the two spindle poles around late pachytene even though the spindle microtubules emanated from both centrosomes. Overall, our work provides new insights into the regulation of centrosome behavior to ensure critical meiotic events and the generation of intact oocytes.     

A novel peptide isolated from the leaves of Gymnema sylvestre--I. Characterization and its suppressive effect on the neural responses to sweet taste stimuli in the rat.

1. A new substance that suppressed selectively the neural responses of the rat to sweet taste stimuli was isolated from the leaves of Gymnema sylvestre. 2. The substance was proved to be a peptide consisting of 35 amino acids and having a molecular weight of about 4,000. 3. The inhibitory effect on the sweet responses appeared after treating the tongue surface with the peptide at a concentration of more than 1 x 10(-6) M.     

Editor's choice: Large,Male Germ Cell-Specific Hypomethylated DNA Domains With Unique Genomic and Epigenomic Features on the Mouse X Chromosome

To understand the epigenetic regulation required for germ cell-specific gene expression in the mouse, we analysed DNA methylation profiles of developing germ cells using a microarray-based assay adapted for a small number of cells. The analysis revealed differentially methylated sites between cell types tested. Here, we focused on a group of genomic sequences hypomethylated specifically in germline cells as candidate regions involved in the epigenetic regulation of germline gene expression. These hypomethylated sequences tend to be clustered, forming large (10 kb to ∼9 Mb) genomic domains, particularly on the X chromosome of male germ cells. Most of these regions, designated here as large hypomethylated domains (LoDs), correspond to segmentally duplicated regions that contain gene families showing germ cell- or testis-specific expression, including cancer testis antigen genes. We found an inverse correlation between DNA methylation level and expression of genes in these domains. Most LoDs appear to be enriched with H3 lysine 9 dimethylation, usually regarded as a repressive histone modification, although some LoD genes can be expressed in male germ cells. It thus appears that such a unique epigenomic state associated with the LoDs may constitute a basis for the specific expression of genes contained in these genomic domains.