During development from the fertilized egg to a multicellular organism, cell fate decisions have to be taken and cell lineage or tissue-specific gene expression patterns are created and maintained. These alterations in gene expression occur in the context of chromatin structure and are controlled by chromatin modifying enzymes. Gene disruption studies in different genetic systems have shown an essential role of various histone deacetylases (HDACs) during early development and cellular differentiation. In this review, we focus on the functions of the class I enzymes HDAC1 and HDAC2 during development in different organisms and summarise the current knowledge about their involvement in neurogenesis, myogenesis, haematopoiesis and epithelial cell differentiation.
KEY WORDS: HDAC1, HDAC2, chromatin, differentiation, development
Histone deacetylasesPosttranslational modifications of histones cause changes in the accessibility of DNA, thereby regulating many important cellular processes including transcription. Acetylation of core histones leads to a change in the net positive charge of histone tails and local opening of chromatin structure, a feature of transcriptionally active genes. On the other hand, deacetylated histone tails interact more closely with DNA and lead to a repressive state. Histone deacetylases (HDACs) catalyse the removal of acetyl groups from histone tails and are therefore considered as transcriptional corepressors. In addition to histones, HDACs also deacetylate non-histone proteins, such as the cytoskeletal protein tubulin (Hubbert et al., 2002) or transcription factors including p53 (Luo et al., 2000), E2F1 (MartinezBalbas et al., 2000) and YY1 (Yao et al., 2001). In fact, phylogenetic analysis suggests that the enzymatic activity was initially directed against non-histone proteins in a common ancestor devoid of histones (Gregoretti et al., 2004). In mammals, 18 deacetylases have been identified so far. These enzymes have been divided into 4 classes based on sequence similarity: Classic HDACs comprise class I (Saccharomyces cerevisiae Rpd3-like), class II (Saccharomyces cerevisiae Hda1-like) and class IV (HDAC11-like) enzymes. Class III consists of NAD-dependent, functionally unrelated Sir2-like deacetylases Int. J. Dev. Biol. 53: 275-289 (2009) Abbreviations used in this paper: HAT, histone acetyltransferase; HDA, HDAC, histone deacetylase; HDI, HDAC inhibitor; NuRD, nucleosome remodelling and deacetylase complex; Rpd3, reduced potassium dependency 3.named "sirtuins". Class I, II and IV HDACs are members of an ancient enzyme family, highly conserved throughout eukaryotic and prokaryotic evolution and are found in animals, plants, fungi, archaebacteria and eubacteria (Gregoretti et al., 2004).
Class I histone deacetylasesPhylogenetic analysis revealed that class I genes in animals can be grouped into HDAC1/HDAC2, HDAC3 and HDAC8-like genes. Members of each subclass have been identified in protostomia (Oger et al., 2008) and deuterostomia. Species analysed so far carry orthologs (...