The C-terminal domains of human TNRC6A,TNRC6B,and TNRC6C silence bound transcripts independently of Argonaute proteins

Proteins of the GW182 family are essential components of the miRNA pathway in animal cells. Vertebrate genomes encode three GW182 paralogs (TNRC6A, TNRC6B, and TNRC6C), which may be functionally redundant. Here, we show that the N-terminal GW-repeat-containing regions of all three TNRC6s interact with the four human Argonaute proteins (AGO1–AGO4). We also show that TNRC6A, TNRC6B, and TNRC6C silence the expression of bound mRNAs. This activity is mediated by their C-terminal silencing domains, and thus, is independent of the interaction with AGO1–AGO4. Silencing by TNRC6A, TNRC6B, and TNRC6C is effected by changes in protein expression and mRNA stability that can, in part, be attributed to deadenylation. Our findings indicate that TNRC6A, TNRC6B, and TNRC6C are recruited to miRNA targets through an interaction between their N-terminal domain and an Argonaute protein; the TNRC6s then promote translational repression and/or degradation of miRNA targets through a C-terminal silencing domain.     

Glutamine synthetase sequence evolution in the mycobacteria and their use as molecular markers for Actinobacteria speciation

Background  

Although the gene encoding for glutamine synthetase (gln A) is essential in several organisms, multiple glnA copies have been identified in bacterial genomes such as those of the phylum Actinobacteria, notably the mycobacterial species. Intriguingly, previous reports have shown that only one copy (gln A1) is essential for growth in M. tuberculosis, while the other copies (gln A2, gln A3 and gln A4) are not.     

Retinoylation of the type II cAMP-binding regulatory subunit of cAMP-dependent protein kinase is increased in psoriatic human fibroblasts

Previously, we have reported a defect in the cAMP-dependent protein kinases (cAMP-PK) in psoriatic cells (i.e., a decrease in 8-azido-[³²P]cAMP binding to the regulatory subunits and a decrease in phosphotransferase activity) which is rapidly reversed with retinoic acid (RA) treatment of these cells. This led us to examine a possible direct interaction between retinoids and the RI and RII regulatory subunits through retinoylation. Retinoylation of RI and RII present in normal and psoriatic human fibroblasts was analysed by [³H]RA treatment of these cells, followed either by chromatographic separation of the regulatory subunits or by their specific immunoprecipitation. These studies indicated that RI and RII can be retinoylated. [³H]RA labeling of the RII subunit was significantly (P < 0.005) greater in psoriatic fibroblasts (nine subjects; mean 7.47 relative units ± 1.37 SEM) compared to normal fibroblasts (eight subjects; mean 2.46 relative units ± 0.49 SEM). [³H]RA labeling of and the increase in 8-azido-[³²P]-binding to the RI and RII subunit in psoriatic fibroblasts showed a similar time course. This suggests that the rapid effect of retinoic acid treatment to enhance 8-azido-[³²P]-cAMP binding to the RI and RII in psoriatic fibroblasts may be due, in part, to covalent modification of the regulatory subunits by retinoylation. © 1996 Wiley-Liss, Inc.     

Monthly day/night changes and seasonal daily rhythms of sexual steroids in Senegal sole (Solea senegalensis) under natural fluctuating or controlled environmental conditions

In this paper we attempted to investigate the existence of daily fluctuations on plasma sexual steroids (17beta-estradiol, E(2) and testosterone, T) in Senegal sole (Solea senegalensis) females. We described the monthly day/night concentrations and seasonal daily rhythms in animals reared under natural photo- and thermo-period. In addition, the influence of the natural annual fluctuation of the water temperature on the plasma concentration of these steroids was investigated, using one group of Senegal sole under a natural photoperiod, but with an attenuated thermal cycle (around 17-20 degrees C) for one year. Although no significant day/night differences were detected in monthly samplings, the existence of an annual rhythm of E(2) and T (p<0.01) with an acrophase in February was revealed by COSINOR analysis. Maximum values were reached in March for both steroids (6.1+/-1.7 ng mL(-1) at mid-dark, MD and 4.0+/-0.6 ng mL(-1) at mid-light, ML for E2 and 1.4+/-0.4 ng mL(-1) at MD and 0.8+/-0.1 ng mL(-1) at ML for T) in anticipation of the spawning season (May-June). As regards seasonal daily rhythms, the presence of daily oscillations was revealed. At the spring solstice (21st March) a daily rhythm was observed for both steroids (COSINOR, p<0.01), with an acrophase at 20:00 h (E(2)) and at 21:08 h (T). In summer, autumn and winter no daily rhythms were observed due to the low steroid levels at those seasons. When Senegal sole females were submitted to an attenuated annual thermal cycle, the steroid rhythm disappeared (there was no surge in spring, as in the control group) and these fish did not spawn, despite being subjected to natural photoperiod conditions. This result underlined the importance of the natural annual fluctuation of water temperature and photoperiod on the synchronization of the spawning season and on the onset of steroidogenesis.     

Differences in Diet Between Six Neighbouring Groups of Vervet Monkeys

The comparative approach provides a powerful tool to study evolutionary questions on both intra‐ and interspecific variation. It has been applied to a great variety of taxa, including primates. Primate studies differ from those on most other taxa in two ways: first, data from most study sites contain information about only one group. Second, primatologists have used the comparative approach also to identify local traditions, that is, behaviours that spread through social learning. Here, we evaluate the appropriateness of such data by comparing the diet composition of six neighbouring groups of vervet monkeys, Cercopithecus aethiops. We used scan samples to collect diet data, and abundance measures and phenology to assess the availability of the 14 most important tree species utilised during the study. We calculated indices of diet overlap, which were highly variable and could be remarkably low. Furthermore, we found significant differences between group diets with respect to the relative utilisation of 13 of the 14 tree species. For all 13 species, we found positive correlations between local abundance and appearance in the diet, consistent with the importance of local ecology for diet composition. Nevertheless, more detailed comparisons of pairs of groups often revealed significant mismatches between the relative importance of a tree species and its local abundance. In conclusion, local variation merits increased attention by primatologists. While our results are compatible with the possibility that traditions exist on a local (group) rather than population scale, alternative explanations have to be considered.