HBO1 Is Required for H3K14 Acetylation and Normal Transcriptional Activity during Embryonic Development

Abstract

We report here that the MYST histone acetyltransferase HBO1 (histone acetyltransferase bound to ORC; MYST2/KAT7) is essential for postgastrulation mammalian development. Lack of HBO1 led to a more than 90% reduction of histone 3 lysine 14 (H3K14) acetylation, whereas no reduction of acetylation was detected at other histone residues. The decrease in H3K14 acetylation was accompanied by a decrease in expression of the majority of genes studied. However, some genes, in particular genes regulating embryonic patterning, were more severely affected than "housekeeping" genes. Development of HBO1-deficient embryos was arrested at the 10-somite stage. Blood vessels, mesenchyme, and somites were disorganized. In contrast to previous studies that reported cell cycle arrest in HBO1-depleted cultured cells, no defects in DNA replication or cell proliferation were seen in Hbo1 mutant embryo primary fibroblasts or immortalized fibroblasts. Rather, a high rate of cell death and DNA fragmentation was observed in Hbo1 mutant embryos, resulting initially in the degeneration of mesenchymal tissues and ultimately in embryonic lethality. In conclusion, the primary role of HBO1 in development is that of a transcriptional activator, which is indispensable for H3K14 acetylation and for the normal expression of essential genes regulating embryonic development.In general, acetylation of histone lysine residues correlates positively and strongly with transcriptionally active regions of the genome (37, 49, 54); in contrast, heterochromatin is hypoacetylated (7,8). It has been proposed that particular patterns of posttranslational histone modifications represent a "code" and that histone modifications are recognized by transcription factors via specific chromatin-binding domains (2,31,60,68). Indeed, acetylated lysines are recognized by bromodomains (13, 30). However, histones can be acetylated at multiple sites, and with few exceptions, very little is known about the biological function of acetylation at specific histone lysine residues in multicellular organisms. Moreover, the residue specificity of few histone acetyltransferases has been characterized in vertebrate organisms. Two members of the MYST family of histone acetyltransferases, MOF (MYST1/KAT8) and MOZ (MYST3/ KAT6A), have highly restricted substrate specificities in vivo.In Drosophila melanogaster and mice in vivo, as well as in human cells in vitro, MOF is specifically required for acetylation of histone 4 lysine 16 (H4K16) (3, 61, 64), whereas MOZ has a specific role in the acetylation of H3K9 in Hox gene clusters (69). Since embryonic development is dependent on the precise regulation of temporal-spatial patterns of gene expression, establishing the correct pattern of histone acetylation at developmentally important gene loci is critical. Accordingly, MOF and MOZ, as well two other MYST family members, QKF (MORF/MYST4/KAT6B) and TIP60 (KAT5), have distinct and essential functions during mammalian development (21,24,34,47,63,64,67,69). We show here that the MYST histone acety...

Exchange of associated factors directs a switch in HBO1 acetyltransferase histone tail specificity

“…We even showed that HBO1 siRNA-mediated knockdown in HeLa cells leads to a global loss of H4 acetylation on Lys5, Lys8, and Lys12, matching in vitro specificity on chromatin and arguing that HBO1 was the main H4-specific HAT in mammals (Doyon et al 2006). On the other hand, it was later shown that HBO1 gene knockout in mouse embryos leads instead to a loss of bulk H3K14ac in primary embryonic fibroblasts at embryonic day 9.5 (E9.5), while H4 acetylation persisted (Kueh et al 2011). In addition, a HBO1-BRPF2 complex was reported in K562 leukemic cells and shown to target global H3K14 acetylation and erythroid regulators (Mishima et al 2011).…”

“…It is important to point out that HBO1 is nevertheless confirmed as a major mammalian HAT, since its depletion leads to global loss of histone acetylation on H3 in mouse erythroblasts/embryonic fibroblasts or on H4 in HeLa cells (Doyon et al 2006;Kueh et al 2011;Mishima et al 2011). It will be very interesting to determine what is responsible for bulk H4 acetylation in Hbo1 À/À mouse embryonic fibroblasts (Kueh et al 2011). Is it Tip60?…”

Conserved Molecular Interactions within the HBO1 Acetyltransferase Complexes Regulate Cell Proliferation

“…In this study, we uncovered the conserved structural determinants for assembly of these complexes and their interaction with chromatin. By focusing our efforts on the human HBO1 complex, a major source of histone H4 and H3 acetylation in vivo (8,23), we identified two short regions conserved in a subunit present in all MYST-ING complexes that are responsible for physical association of the MYST HAT enzyme and the ING tumor suppressor. In a separate study on the MOZ/MORF complexes, deletions affecting these short conserved domains in the BRPF1 subunit also disrupted complex assembly (65).…”

“…We focused on the human ING4/5 tetrameric complexes that contain the HBO1 HAT and JADE1/2/3 paralogues (Fig. 1A), as they constitute one of the major sources of histone H4 and H3 acetylation in vivo (8,23,68). Notably, we identified two short domains conserved in all MYST-ING complexes that act as a scaffold for complex assembly.…”

Histone target selection within chromatin: an exemplary case of teamwork

“…For example, complete depletion of the MOZ acetyltransferase in mouse embryos decreases the acetylation of H3K9 at specific genomic loci, although the MOZ complex has been shown to acetylate H3K14 in chromatin (Doyon et al 2006;Ullah et al 2008;Voss et al 2009;Lalonde et al 2013). Furthermore, while depletion of the HBO1 acetyltransferase by siRNAs in HeLa or H1299 cells leads to a significant decrease of H4 acetylation (K5, K8, and K12) and appears to have an impact on cell cycle progression into S phase (Doyon et al 2006;Miotto and Struhl 2010;Havasi et al 2013), its complete knockout in mouse embryos shows only a loss of H3K14ac in mouse embryonic fibroblasts with no apparent replicative defect (Kueh et al 2011). These differential phenotypes indicate that chromatin modifiers can also have tissue-specific activities and that the expression level of associated factors in different tissues or cell lines may influence their function.…”