Knockout experiments in Tetrahymena show that linker histone H1 is not essential for nuclear assembly or cell viability. These results, together with a series of biochemical and cell biological observations, challenge the existing paradigm that requires linker histones to be a key organizing component of higher‐order chromatin structure. The H1 Knockouts also reveal a much more subtle role for H1. Instead of acting as a general transcriptional repressor, H1 is found to regulate a limited number of specific genes. Surprisingly, H1 (...) can both activate and repress transcription. We discuss how this architectural protein might accomplish this important regulatory role. (shrink)

It is becoming clear that the post‐translational modification of histone and non‐histone proteins by acetylation is part of an important cellular signaling process controling a wide variety of functions in both the nucleus and the cytoplasm. Recent investigations designate this signaling pathway as one of the primary targets of viral proteins after infection. Indeed, specific viral proteins have acquired the capacity to interact with cellular acetyltransferases (HATs) and deacetylases (HDACs) and consequently to disrupt normal acetylation signaling pathways, thereby affecting viral (...) and cellular gene expression. Here we review the targeting of cellular HATs and HDACs by viral proteins and highlight different strategies adopted by viruses to control cellular acetylation signaling and to accomplish their life cycle. BioEssays 25:58–65, 2003. © 2002 Wiley Periodicals, Inc. (shrink)

Despite the progress achieved over the last decade after the birth of the first cloned mammal, the efficiency of reproductive cloning remains invariably low. However, research aiming at the use of nuclear transfer for the production of patient‐tailored stem cells for cell/tissue therapy is progressing rapidly. Yet, reproductive cloning has many potential implications for animal breeding, transgenic research and the conservation of endangered species. In this article we suggest that the changes in the epi‐/genotype observed in cloned embryos arise from (...) unbalanced nuclear reprogramming between parental chromosomes. It is probable that the oocyte reprogramming machinery, devised for resident chromosomes, cannot target the paternal alleles of somatic cells. We, therefore, suggest that a reasonable approach to balance this asymmetry in nuclear reprogramming might involve the transient expression in donor cells of chromatin remodelling proteins, which are physiologically expressed during spermatogenesis, in order to induce a male‐specific chromatin organisation in the somatic cells before nuclear transfer. BioEssays 30:66–74, 2008. © 2007 Wiley Periodicals, Inc. (shrink)

The haploid male germ cell differentiation program controls essential steps of male gametogenesis and relies partly on a significant number of sex chromosome‐linked genes. These genes need to escape chromosome‐wide transcriptional repression of sex chromosomes, which occurs during meiosis and is largely maintained in post‐meiotic cells. A newly discovered histone lysine modification, crotonylation (Kcr), marks X/Y‐linked genes that are active in post‐meiotic male germ cells. Histone Kcr, by conferring resistance to transcriptional repressors, could be a dominant element in maintaining these (...) genes active in the globally repressive environment of haploid cell sex chromosomes. Furthermore, the same mark was found associated with post‐meiotically activated genes on autosomes. Histone Kcr therefore appears to be an indicator of the male haploid cell gene expression program and a notable element of genome programming in the post‐meiotic phases of spermatogenesis. (shrink)