Chromatin-modifying complexes are important for transcriptional control, but their roles in the regulation of development are poorly understood. Here, we show that components of the nucleosome remodelling and histone deacetylase (NURD) complex [1] [2] [3] [4] [5] antagonise vulval development, which is induced by the Ras signal transduction pathway. In three of the six equivalent vulval precursor cells, the Ras pathway is active, leading to the production of vulval fates [6]; in the remaining three, the Ras pathway is inhibited and vulval fates repressed. Inhibition of Ras signaling occurs in part through the action of the synthetic multivulval (synMuv) genes, which comprise two functionally redundant pathways (synMuvA and synMuvB) [7]. We found that five Caenorhabditis elegans members of the NURD chromatin remodelling complex inhibit vulval development through both the synMuvA and synMuvB pathways (hda-1, rba-1, lin-53, chd-3 and chd-4); a further two members, the MTA1-related genes egr-1 and egl-27, act only in the synMuvA pathway. We propose that the synMuvA and synMuvB pathways function redundantly to recruit or activate a core NURD complex, which then represses vulval developmental target genes by local histone deacetylation. These results emphasise the importance of chromatin regulation in developmental decisions. Furthermore, inhibition of Ras signaling suggests a possible link between NURD function and cancer.

SUMMARYEpithelial tubes perform functions that are essential for the survival of multicellular organisms. Understanding how their polarised features are maintained is therefore crucial. By analysing the function of the clathrin adaptor AP-1 in the C. elegans intestine, we found that AP-1 is required for epithelial polarity maintenance. Depletion of AP-1 subunits does not affect epithelial polarity establishment or the formation of the intestinal lumen. However, the loss of AP-1 affects the polarised distribution of both apical and basolateral transmembrane proteins. Moreover, it triggers de novo formation of ectopic apical lumens between intestinal cells along the lateral membranes later during embryogenesis. We also found that AP-1 is specifically required for the apical localisation of the small GTPase CDC-42 and the polarity determinant PAR-6. Our results demonstrate that AP-1 controls an apical trafficking pathway required for the maintenance of epithelial polarity in vivo in a tubular epithelium.

The protein deacetylase SIRT1, and its activator resveratrol, exert beneficial effects on glucose metabolism. Different SIRT1 targets have been identified, including PTP1B, AMPK, FOXO, PGC-1α and IRS2. The latter may underscore a tight link between SIRT1 and insulin signaling components. However, whether SIRT1 has a direct effect on insulin resistance and whether resveratrol acts directly or indirectly in this context is still a matter of controversy and this question has not been addressed in muscle cells. Here, we show that SIRT1 protein expression is decreased in muscle biopsies and primary myotubes derived from type 2 diabetic patients, suggesting a contribution of diminished SIRT1 in the determination of muscle insulin resistance. To investigate the functional impact of SIRT1 on the insulin pathway, the activation of insulin downstream effector PKB was evaluated after SIRT1 inactivation by RNAi, SIRT1 overexpression, or resveratrol treatments. In muscle cells and HEK293 cells, downregulation of SIRT1 reduced, while overexpression increased, insulin-induced PKB activatory phosphorylation. Further molecular characterisation revealed that SIRT1 interacts in an insulin-independent manner with the PI3K adapter subunit p85. We then investigated whether resveratrol may improve insulin signaling in muscle cells via SIRT1, or alternative targets. Incubation of muscle cells with resveratrol reverted the insulin-resistant state induced by prolonged TNFα or insulin treatment. Resveratrol-dependent improvement of insulin-resistance occurred through inhibition of serine phosphorylation of IRS1/2, implicating resveratrol as a serine kinase inhibitor. Finally, a functional interaction between PI3K and SIRT1 was demonstrated in C. elegans, where constitutively active PI3K - mimicking increased IIS signaling - lead to shortened lifespan, while removal of sir-2.1 abolished PI3K-induced lifespan shortening. Our data identify SIRT1 as a positive modulator of insulin signaling in muscle cells through PI3K, and this mechanism appears to be conserved from C. elegans through humans.