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International audience; Because regulation of its activity is instrumental either to support cell proliferation and growth or to promote cell death, the universal myo-inositol phosphate synthase (MIPS), responsible for myo-inositol biosynthesis, is a critical enzyme of primary metabolism. Surprisingly, we found this enzyme to be imported in the nucleus and to interact with the histone methyltransferases ATXR5 and ATXR6, raising the question of whether MIPS1 has a function in transcriptional regulation. Here, we demonstrate that MIPS1 binds directly to its promoter to stimulate its own expression by locally inhibiting the spreading of ATXR5/6-dependent heterochromatin marks coming from a transposable element. Furthermore, on activation of pathogen response, MIPS1 expression is reduced epigenetically, providing evidence for a complex regulatory mechanism acting at the transcriptional level. Thus, in plants, MIPS1 appears to have evolved as a protein that connects cellular metabolism, pathogen response and chromatin remodeling.

International audience; MicroRNAs are tiny RNA molecules that play important regulatory roles in a broad range of developmental, physiological or pathological processes. Despite recent progress in our understanding of miRNA processing and biological functions, little is known about the regulatory mechanisms that control their expression at the transcriptional level. C19MC is the largest human microRNA gene cluster discovered to date. This 100-kb long cluster consists of 46 tandemly repeated, primate-specific pre-miRNA genes that are flanked by Alu elements (Alus) and embedded within a approximately 400- to 700-nt long repeated unit. It has been proposed that C19MC miRNA genes are transcribed by RNA polymerase III (Pol-III) initiating from A and B boxes embedded in upstream Alu repeats. Here, we show that C19MC miRNAs are intron-encoded and processed by the DGCR8-Drosha (Microprocessor) complex from a previously unidentified, non-protein-coding Pol-II (and not Pol-III) transcript which is mainly, if not exclusively, expressed in the placenta.

International audience; An interference assay has been devised in Schizosaccharomyces pombe to rapidly identify and clone genes involved in chromosome segregation. Random S.pombe cDNAs were overexpressed from an inducible promoter in a strain carrying an additional, non-essential minichromosome. Overexpression of cDNAs derived from four genes, two known (nda3+and ubc4+, encoding beta-tubulin and a ubiquitin conjugating enzyme, respectively) and two unknown, named mlo2+ and mlo3+ (missegregation & lethal when over expressed) caused phenotypes consistent with a failure to segregate chromosomes. Full overexpression of all four cDNAs was lethal. Cells overexpressing nda3+ and ubc4+ cDNAs arrested with condensed unsegregated chromosomes and cells overexpressing mlo2+ displayed an asymmetric distribution of nuclear chromatin. Sublethal levels of overexpression of nda3+, ubc4+ and mlo2+ cDNAs caused elevated rates of minichromosome loss. A third cDNA mlo3+, displayed no increase in the frequency of minichromosome loss at sublethal levels of overexpression but full overexpression caused a complete failure to segregate chromosomes. Our results confirm the assumption that beta-tubulin overexpression is lethal in S.pombe, implicate ubc4+ in the control of metaphase-anaphase transition in fission yeast and finally identify two new genes, mlo2+and mlo3+, likely to play an important role for chromosome transmission fidelity in mitosis.