D espite the fact that it has been intensively studied during the last decade, the function of th... more D espite the fact that it has been intensively studied during the last decade, the function of the histone variant H2A.Z remains enigmatic. In the last few years, we and others have determined the localization of H2A.Z in various organisms. These studies have revealed that H2A.Z occupies different well defined regions in the genome. Interestingly, H2A.Z occupies the promoters and regulatory regions of active genes, as well as constitutive and facultative heterochromatin. The localization of H2A.Z on genomic regions with so diverse functions suggests that the roles of H2A.Z are multiple, only increasing the mystery around this molecule. The way H2A.Z finds its way into these regions is not fully understood but mechanisms that direct the specific incorporation of H2A.Z in promoters and enhancers have been well described. In this Point of View, we review our recent work suggesting that non-targeted incorporation, coupled to targeted depletion of H2A.Z, is a novel mechanism for localizing H2A.Z to some regions. We propose that the various functions of H2A.Z may be a consequence of the mechanism used for its incorporation, as well as its interactions with other histone variants.
Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caus... more Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caused by a polyglutamine (polyQ) expansion, but it is the only one in which the retina is affected. Increasing evidence suggests that transcriptional alterations contribute to polyQ pathogenesis, although the mechanism is unclear. We previously demonstrated that the SCA7 gene product, ataxin-7 (ATXN7), is a subunit of the GCN5 histone acetyltransferasecontaining coactivator complexes TFTC/STAGA. We show here that TFTC/STAGA complexes purified from SCA7 mice have normal TRRAP, GCN5, TAF12, and SPT3 levels and that their histone or nucleosomal acetylation activities are unaffected. However, rod photoreceptors from SCA7 mouse models showed severe chromatin decondensation. In agreement, polyQ-expanded ataxin-7 induced histone H3 hyperacetylation, resulting from an increased recruitment of TFTC/STAGA to specific promoters. Surprisingly, hyperacetylated genes were transcriptionally down-regulated, and expression analysis revealed that nearly all rod-specific genes were affected, leading to visual impairment in SCA7 mice. In conclusion, we describe here a set of events accounting for SCA7 pathogenesis in the retina, in which polyQexpanded ATXN7 deregulated TFTC/STAGA recruitment to a subset of genes specifically expressed in rod photoreceptors, leading to chromatin alterations and consequent progressive loss of rod photoreceptor function. Citation: Helmlinger D, Hardy S, Abou-Sleymane G, Eberlin A, Bowman AB, et al. (2006) Glutamine-expanded ataxin-7 alters TFTC/STAGA recruitment and chromatin structure leading to photoreceptor dysfunction. PLoS Biol 4(3): e67.
Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caus... more Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caused by a polyglutamine (polyQ) expansion, but it is the only one in which the retina is affected. Increasing evidence suggests that transcriptional alterations contribute to polyQ pathogenesis, although the mechanism is unclear. We previously demonstrated that the SCA7 gene product, ataxin-7 (ATXN7), is a subunit of the GCN5 histone acetyltransferasecontaining coactivator complexes TFTC/STAGA. We show here that TFTC/STAGA complexes purified from SCA7 mice have normal TRRAP, GCN5, TAF12, and SPT3 levels and that their histone or nucleosomal acetylation activities are unaffected. However, rod photoreceptors from SCA7 mouse models showed severe chromatin decondensation. In agreement, polyQ-expanded ataxin-7 induced histone H3 hyperacetylation, resulting from an increased recruitment of TFTC/STAGA to specific promoters. Surprisingly, hyperacetylated genes were transcriptionally down-regulated, and expression analysis revealed that nearly all rod-specific genes were affected, leading to visual impairment in SCA7 mice. In conclusion, we describe here a set of events accounting for SCA7 pathogenesis in the retina, in which polyQexpanded ATXN7 deregulated TFTC/STAGA recruitment to a subset of genes specifically expressed in rod photoreceptors, leading to chromatin alterations and consequent progressive loss of rod photoreceptor function. Citation: Helmlinger D, Hardy S, Abou-Sleymane G, Eberlin A, Bowman AB, et al. (2006) Glutamine-expanded ataxin-7 alters TFTC/STAGA recruitment and chromatin structure leading to photoreceptor dysfunction. PLoS Biol 4(3): e67.
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder caused by a CAG repeat expan... more Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder caused by a CAG repeat expansion in the SCA7 gene leading to elongation of a polyglutamine tract in ataxin-7, a protein of unknown function. A putative ataxin-7 yeast orthologue (SGF73) has been recently identified as a new component of the SAGA (Spt/Ada/Gcn5 acetylase) multisubunit complex, a coactivator required for transcription of a subset of RNA polymerase II-dependent genes.
A role for variant histone H2A.Z in gene expression is now well established but little is known a... more A role for variant histone H2A.Z in gene expression is now well established but little is known about the mechanisms by which it operates. Using a combination of ChIP-chip, knockdown and expression profiling experiments, we show that upon gene induction, human H2A.Z associates with gene promoters and helps in recruiting the transcriptional machinery. Surprisingly, we also found that H2A.Z is randomly incorporated in the genome at low levels and that active transcription antagonizes this incorporation in transcribed regions. After cessation of transcription, random H2A.Z quickly reappears on genes, demonstrating that this incorporation utilizes an active mechanism. Within facultative heterochromatin, we observe a hyper accumulation of the variant histone, which might be due to the lack of transcription in these regions. These results show how chromatin structure and transcription can antagonize each other, therefore shaping chromatin and controlling gene expression.
D espite the fact that it has been intensively studied during the last decade, the function of th... more D espite the fact that it has been intensively studied during the last decade, the function of the histone variant H2A.Z remains enigmatic. In the last few years, we and others have determined the localization of H2A.Z in various organisms. These studies have revealed that H2A.Z occupies different well defined regions in the genome. Interestingly, H2A.Z occupies the promoters and regulatory regions of active genes, as well as constitutive and facultative heterochromatin. The localization of H2A.Z on genomic regions with so diverse functions suggests that the roles of H2A.Z are multiple, only increasing the mystery around this molecule. The way H2A.Z finds its way into these regions is not fully understood but mechanisms that direct the specific incorporation of H2A.Z in promoters and enhancers have been well described. In this Point of View, we review our recent work suggesting that non-targeted incorporation, coupled to targeted depletion of H2A.Z, is a novel mechanism for localizing H2A.Z to some regions. We propose that the various functions of H2A.Z may be a consequence of the mechanism used for its incorporation, as well as its interactions with other histone variants.
Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caus... more Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caused by a polyglutamine (polyQ) expansion, but it is the only one in which the retina is affected. Increasing evidence suggests that transcriptional alterations contribute to polyQ pathogenesis, although the mechanism is unclear. We previously demonstrated that the SCA7 gene product, ataxin-7 (ATXN7), is a subunit of the GCN5 histone acetyltransferasecontaining coactivator complexes TFTC/STAGA. We show here that TFTC/STAGA complexes purified from SCA7 mice have normal TRRAP, GCN5, TAF12, and SPT3 levels and that their histone or nucleosomal acetylation activities are unaffected. However, rod photoreceptors from SCA7 mouse models showed severe chromatin decondensation. In agreement, polyQ-expanded ataxin-7 induced histone H3 hyperacetylation, resulting from an increased recruitment of TFTC/STAGA to specific promoters. Surprisingly, hyperacetylated genes were transcriptionally down-regulated, and expression analysis revealed that nearly all rod-specific genes were affected, leading to visual impairment in SCA7 mice. In conclusion, we describe here a set of events accounting for SCA7 pathogenesis in the retina, in which polyQexpanded ATXN7 deregulated TFTC/STAGA recruitment to a subset of genes specifically expressed in rod photoreceptors, leading to chromatin alterations and consequent progressive loss of rod photoreceptor function. Citation: Helmlinger D, Hardy S, Abou-Sleymane G, Eberlin A, Bowman AB, et al. (2006) Glutamine-expanded ataxin-7 alters TFTC/STAGA recruitment and chromatin structure leading to photoreceptor dysfunction. PLoS Biol 4(3): e67.
Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caus... more Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caused by a polyglutamine (polyQ) expansion, but it is the only one in which the retina is affected. Increasing evidence suggests that transcriptional alterations contribute to polyQ pathogenesis, although the mechanism is unclear. We previously demonstrated that the SCA7 gene product, ataxin-7 (ATXN7), is a subunit of the GCN5 histone acetyltransferasecontaining coactivator complexes TFTC/STAGA. We show here that TFTC/STAGA complexes purified from SCA7 mice have normal TRRAP, GCN5, TAF12, and SPT3 levels and that their histone or nucleosomal acetylation activities are unaffected. However, rod photoreceptors from SCA7 mouse models showed severe chromatin decondensation. In agreement, polyQ-expanded ataxin-7 induced histone H3 hyperacetylation, resulting from an increased recruitment of TFTC/STAGA to specific promoters. Surprisingly, hyperacetylated genes were transcriptionally down-regulated, and expression analysis revealed that nearly all rod-specific genes were affected, leading to visual impairment in SCA7 mice. In conclusion, we describe here a set of events accounting for SCA7 pathogenesis in the retina, in which polyQexpanded ATXN7 deregulated TFTC/STAGA recruitment to a subset of genes specifically expressed in rod photoreceptors, leading to chromatin alterations and consequent progressive loss of rod photoreceptor function. Citation: Helmlinger D, Hardy S, Abou-Sleymane G, Eberlin A, Bowman AB, et al. (2006) Glutamine-expanded ataxin-7 alters TFTC/STAGA recruitment and chromatin structure leading to photoreceptor dysfunction. PLoS Biol 4(3): e67.
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder caused by a CAG repeat expan... more Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder caused by a CAG repeat expansion in the SCA7 gene leading to elongation of a polyglutamine tract in ataxin-7, a protein of unknown function. A putative ataxin-7 yeast orthologue (SGF73) has been recently identified as a new component of the SAGA (Spt/Ada/Gcn5 acetylase) multisubunit complex, a coactivator required for transcription of a subset of RNA polymerase II-dependent genes.
A role for variant histone H2A.Z in gene expression is now well established but little is known a... more A role for variant histone H2A.Z in gene expression is now well established but little is known about the mechanisms by which it operates. Using a combination of ChIP-chip, knockdown and expression profiling experiments, we show that upon gene induction, human H2A.Z associates with gene promoters and helps in recruiting the transcriptional machinery. Surprisingly, we also found that H2A.Z is randomly incorporated in the genome at low levels and that active transcription antagonizes this incorporation in transcribed regions. After cessation of transcription, random H2A.Z quickly reappears on genes, demonstrating that this incorporation utilizes an active mechanism. Within facultative heterochromatin, we observe a hyper accumulation of the variant histone, which might be due to the lack of transcription in these regions. These results show how chromatin structure and transcription can antagonize each other, therefore shaping chromatin and controlling gene expression.
Uploads
Papers by sara hardy