Histone H1 is an intrinsic component of chromatin, whose important contribution to chromatin structure is well-established in vitro. Little is known, however, about its functional roles in vivo. Here, we have addressed this question in Drosophila, a model system offering many advantages since it contains a single dH1 variant. For this purpose, RNAi was used to efficiently deplete dH1 in flies. Expression-profiling shows that dH1 depletion affects expression of a relatively small number of genes in a regional manner. Furthermore, depletion up-regulates inactive genes, preferentially those located in heterochromatin, while active euchromatic genes are down-regulated, suggesting that the contribution of dH1 to transcription regulation is mainly structural, organizing chromatin for proper gene-expression regulation. Up-regulated genes are remarkably enriched in transposons. In particular, R1/R2 retrotransposons, which specifically integrate in the rDNA locus, are strongly up-regulated. Actually, depletion increases expression of transposon-inserted rDNA copies, resulting in synthesis of aberrant rRNAs and enlarged nucleolus. Concomitantly, dH1-depleted cells accumulate extra-chromosomal rDNA, show increased H2Av content, stop proliferation and activate apoptosis, indicating that depletion causes genome instability and affects proliferation. Finally, the contributions to maintenance of genome integrity and cell proliferation appear conserved in human hH1s, as their expression rescues proliferation of dH1-depleted cells.
Olivera Vujatovic; Katrin Zaragoza; Alejandro Vaquero; Oscar Reina; Jordi Bernués; Fernando Azorín
Bacterial heat-labile (LT) enterotoxins signal through tightly regulated interactions with host cell gangliosides. LT-IIa and LT-IIb of Escherichia coli bind preferentially to gangliosides with a NeuAcα2-3Galβ1-3GalNAc terminus, with key distinctions in specificity. LT-IIc, a newly discove ... more
Phosphate deficiency is characteristic for many natural habitats, resulting in different physiological responses in plants and bacteria including the replacement of phospholipids by glycolipids and other phosphorous-free lipids. The plant pathogenic bacterium Agrobacterium tumefaciens, whi ... more
A tryptophan side chain was introduced into subsite +1 of family GH-18 (class V) chitinases from Nicotiana tabacum and Arabidopsis thaliana (NtChiV and AtChiC, respectively) by the mutation of a glycine residue to tryptophan (G74W-NtChiV and G75W-AtChiC). The specific activity toward glyco ... more