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Senataxin protects the genome: Implications for neurodegeneration and other abnormalities.

Lavin MF, Yeo AJ, Becherel OJ - Rare Dis (2013)

Bottom Line: Similar to that observed for other autosomal recessive ataxias, this protein protects the integrity of the genome against oxidative and other forms of DNA damage to reduce the risk of neurodegeneration.We also showed that senataxin was localized to the XY body in pachytene cells and was involved in transcriptional silencing of these chromosomes.We discuss here potentially different roles for senataxin in proliferating and post-mitotic cells.

View Article: PubMed Central - PubMed

Affiliation: Queensland Institute of Medical Research; Radiation Biology and Oncology; Brisbane, QLD, Australia ; University of Queensland Centre for Clinical Research; Herston, QLD, Australia.

ABSTRACT
Ataxia oculomotor apraxia type 2 (AOA2) is a rare autosomal recessive disorder characterized by cerebellar atrophy, peripheral neuropathy, loss of Purkinje cells and elevated α-fetoprotein. AOA2 is caused by mutations in the SETX gene that codes for the high molecular weight protein senataxin. Mutations in this gene also cause dominant neurodegenerative disorders. Similar to that observed for other autosomal recessive ataxias, this protein protects the integrity of the genome against oxidative and other forms of DNA damage to reduce the risk of neurodegeneration. Senataxin functions in transcription termination and RNA splicing and it has been shown to resolve RNA/DNA hybrids (R-loops) that arise at transcription pause sites or when transcription is blocked. Recent data suggest that this protein functions at the interface between transcription and DNA replication to minimise the risk of collision and maintain genome stability. Our recent data using SETX gene-disrupted mice revealed that male mice were defective in spermatogenesis and were infertile. DNA double strand-breaks persisted throughout meiosis and crossing-over failed in SETX mutant mice. These changes can be explained by the accumulation of R-loops, which interfere with Holiday junctions and crossing-over. We also showed that senataxin was localized to the XY body in pachytene cells and was involved in transcriptional silencing of these chromosomes. While the defect in meiotic recombination was striking in these animals, there was no evidence of neurodegeneration as observed in AOA2 patients. We discuss here potentially different roles for senataxin in proliferating and post-mitotic cells.

No MeSH data available.


Related in: MedlinePlus

Figure 2. Accumulation of R-loops in Setx−/− germ cells. (A) Immunostaining of testes cross-sections from wildtype (+/+) and Setx knockout (−/−) mice with the S9.6 DNA/RNA (R-loop) antibody. Nuclei were stained with Hoechst 33342. Scale bar, 100µm. Regions 1 and 2 show magnifications. (B) Immunostaining of pachytene spermatocytes from wildtype (+/+) and Setx knockout (−/−) with S9.6 antibody shows a dramatic accumulation of R-loops in senataxin deficient germ cells. SCP3 was used to stain for the synaptonemal complex and identify pachytene stage cells. Scale bar, 20 µm.
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Figure 2: Figure 2. Accumulation of R-loops in Setx−/− germ cells. (A) Immunostaining of testes cross-sections from wildtype (+/+) and Setx knockout (−/−) mice with the S9.6 DNA/RNA (R-loop) antibody. Nuclei were stained with Hoechst 33342. Scale bar, 100µm. Regions 1 and 2 show magnifications. (B) Immunostaining of pachytene spermatocytes from wildtype (+/+) and Setx knockout (−/−) with S9.6 antibody shows a dramatic accumulation of R-loops in senataxin deficient germ cells. SCP3 was used to stain for the synaptonemal complex and identify pachytene stage cells. Scale bar, 20 µm.

Mentions: All of the investigations above have described a role for senataxin in preventing collision between DNA replication forks and ongoing transcription to preserve genome integrity in proliferating cells. However, the major phenotype in AOA2 patients is progressive neurodegeneration in post-mitotic tissue. Under those conditions, ongoing transcription will not encounter DNA replication forks. What then is the role of senataxin in the brain? Vantaggiato et. al.23 provided evidence that senataxin plays a role in neuritogenesis and cytoprotection during neuronal differentiation which is mediated by fibroblast growth factor 8 . However, since this is a progressive disease, it is unlikely that the role of senataxin is restricted to development. To address this further, we disrupted the SETX gene in a mouse model for AOA2, which was the subject matter of our recent publication.24 Unfortunately, we did not observe a neurodegenerative phenotype in the Setx−/− mice and there was no evidence of more subtle behavioral differences in these mice, which limited investigation into the nature of the defect in the brains of these mice. This was not altogether surprising since knockout of several of the genes causing autosomal recessive ataxias in humans fails to re-capitulate the phenotype in mouse models.25 However, we observed that Setx−/− male mice were infertile and fertility was reduced in females. While there is no information on male fertility in AOA2, there are a few reports of hypogonadism in females. Criscuolo et. al.4 reported two patients who entered menopause in early adulthood which was also observed in a separate study.5 Ovarian failure has also been observed in a patient with AOA226 and another patient had a diagnosis of polycystic ovarian syndrome.27 We subsequently showed that senataxin had an essential role in spermatogenesis in mice and in its absence these cells failed to progress past the pachytene stage of prophase 1 of meiosis.24 The DNA double-strand breaks (DSB) introduced by Spo11 in readiness for meiotic recombination were inefficiently repaired on autosomes, resulting in a failure to complete crossing-over. During the process of crossing-over, autosomes remain transcriptionally active, so it was possible that in the absence of senataxin, R-loops would accumulate in the vicinity of unrepaired DNA DSB leading to collapse of Holiday junctions and inhibition of the crossing-over step. Indeed this was the case since we detected elevated levels of R-loops in both spermatocyte spreads and testes sections (Fig. 2). Wild-type mice showed a very much reduced level of signal. So in the case of spermatocyte differentiation, the R-loops that accumulate in the absence of senataxin appear to collide with Holiday junctions rather than with advancing replication forks. We also screened for the presence of R-loops in the brains of Setx mutant mice but failed to detect these structures by immunofluorescence (unpublished data). This was not altogether surprising since neither DNA replication nor DNA recombination is taking place in this tissue. It is possible that persistence of DNA damage in post-mitotic cells might lead to the accumulation of these structures, which in turn could contribute to the neurodegenerative changes in AOA2 patients. However, we and others have provided evidence for a broader role for senataxin in transcription and other cellular processes. Senataxin plays an important role in transcription termination to prevent RNA readthrough, which may or may not be related to R-loop resolution.15,16 The presence of significant readthrough of mRNA may lead to inefficient or aberrant protein synthesis and consequently cell toxicity. Senataxin has also been shown to play a role in the regulation of splicing15 and deficiency of the SR splicing factor ASF/SF2 leads to R-loop accumulation and genome instability.18 This in turn may interfere with the fidelity of the transcriptome in AOA2 cerebellum.


Senataxin protects the genome: Implications for neurodegeneration and other abnormalities.

Lavin MF, Yeo AJ, Becherel OJ - Rare Dis (2013)

Figure 2. Accumulation of R-loops in Setx−/− germ cells. (A) Immunostaining of testes cross-sections from wildtype (+/+) and Setx knockout (−/−) mice with the S9.6 DNA/RNA (R-loop) antibody. Nuclei were stained with Hoechst 33342. Scale bar, 100µm. Regions 1 and 2 show magnifications. (B) Immunostaining of pachytene spermatocytes from wildtype (+/+) and Setx knockout (−/−) with S9.6 antibody shows a dramatic accumulation of R-loops in senataxin deficient germ cells. SCP3 was used to stain for the synaptonemal complex and identify pachytene stage cells. Scale bar, 20 µm.
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Related In: Results  -  Collection

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Figure 2: Figure 2. Accumulation of R-loops in Setx−/− germ cells. (A) Immunostaining of testes cross-sections from wildtype (+/+) and Setx knockout (−/−) mice with the S9.6 DNA/RNA (R-loop) antibody. Nuclei were stained with Hoechst 33342. Scale bar, 100µm. Regions 1 and 2 show magnifications. (B) Immunostaining of pachytene spermatocytes from wildtype (+/+) and Setx knockout (−/−) with S9.6 antibody shows a dramatic accumulation of R-loops in senataxin deficient germ cells. SCP3 was used to stain for the synaptonemal complex and identify pachytene stage cells. Scale bar, 20 µm.
Mentions: All of the investigations above have described a role for senataxin in preventing collision between DNA replication forks and ongoing transcription to preserve genome integrity in proliferating cells. However, the major phenotype in AOA2 patients is progressive neurodegeneration in post-mitotic tissue. Under those conditions, ongoing transcription will not encounter DNA replication forks. What then is the role of senataxin in the brain? Vantaggiato et. al.23 provided evidence that senataxin plays a role in neuritogenesis and cytoprotection during neuronal differentiation which is mediated by fibroblast growth factor 8 . However, since this is a progressive disease, it is unlikely that the role of senataxin is restricted to development. To address this further, we disrupted the SETX gene in a mouse model for AOA2, which was the subject matter of our recent publication.24 Unfortunately, we did not observe a neurodegenerative phenotype in the Setx−/− mice and there was no evidence of more subtle behavioral differences in these mice, which limited investigation into the nature of the defect in the brains of these mice. This was not altogether surprising since knockout of several of the genes causing autosomal recessive ataxias in humans fails to re-capitulate the phenotype in mouse models.25 However, we observed that Setx−/− male mice were infertile and fertility was reduced in females. While there is no information on male fertility in AOA2, there are a few reports of hypogonadism in females. Criscuolo et. al.4 reported two patients who entered menopause in early adulthood which was also observed in a separate study.5 Ovarian failure has also been observed in a patient with AOA226 and another patient had a diagnosis of polycystic ovarian syndrome.27 We subsequently showed that senataxin had an essential role in spermatogenesis in mice and in its absence these cells failed to progress past the pachytene stage of prophase 1 of meiosis.24 The DNA double-strand breaks (DSB) introduced by Spo11 in readiness for meiotic recombination were inefficiently repaired on autosomes, resulting in a failure to complete crossing-over. During the process of crossing-over, autosomes remain transcriptionally active, so it was possible that in the absence of senataxin, R-loops would accumulate in the vicinity of unrepaired DNA DSB leading to collapse of Holiday junctions and inhibition of the crossing-over step. Indeed this was the case since we detected elevated levels of R-loops in both spermatocyte spreads and testes sections (Fig. 2). Wild-type mice showed a very much reduced level of signal. So in the case of spermatocyte differentiation, the R-loops that accumulate in the absence of senataxin appear to collide with Holiday junctions rather than with advancing replication forks. We also screened for the presence of R-loops in the brains of Setx mutant mice but failed to detect these structures by immunofluorescence (unpublished data). This was not altogether surprising since neither DNA replication nor DNA recombination is taking place in this tissue. It is possible that persistence of DNA damage in post-mitotic cells might lead to the accumulation of these structures, which in turn could contribute to the neurodegenerative changes in AOA2 patients. However, we and others have provided evidence for a broader role for senataxin in transcription and other cellular processes. Senataxin plays an important role in transcription termination to prevent RNA readthrough, which may or may not be related to R-loop resolution.15,16 The presence of significant readthrough of mRNA may lead to inefficient or aberrant protein synthesis and consequently cell toxicity. Senataxin has also been shown to play a role in the regulation of splicing15 and deficiency of the SR splicing factor ASF/SF2 leads to R-loop accumulation and genome instability.18 This in turn may interfere with the fidelity of the transcriptome in AOA2 cerebellum.

Bottom Line: Similar to that observed for other autosomal recessive ataxias, this protein protects the integrity of the genome against oxidative and other forms of DNA damage to reduce the risk of neurodegeneration.We also showed that senataxin was localized to the XY body in pachytene cells and was involved in transcriptional silencing of these chromosomes.We discuss here potentially different roles for senataxin in proliferating and post-mitotic cells.

View Article: PubMed Central - PubMed

Affiliation: Queensland Institute of Medical Research; Radiation Biology and Oncology; Brisbane, QLD, Australia ; University of Queensland Centre for Clinical Research; Herston, QLD, Australia.

ABSTRACT
Ataxia oculomotor apraxia type 2 (AOA2) is a rare autosomal recessive disorder characterized by cerebellar atrophy, peripheral neuropathy, loss of Purkinje cells and elevated α-fetoprotein. AOA2 is caused by mutations in the SETX gene that codes for the high molecular weight protein senataxin. Mutations in this gene also cause dominant neurodegenerative disorders. Similar to that observed for other autosomal recessive ataxias, this protein protects the integrity of the genome against oxidative and other forms of DNA damage to reduce the risk of neurodegeneration. Senataxin functions in transcription termination and RNA splicing and it has been shown to resolve RNA/DNA hybrids (R-loops) that arise at transcription pause sites or when transcription is blocked. Recent data suggest that this protein functions at the interface between transcription and DNA replication to minimise the risk of collision and maintain genome stability. Our recent data using SETX gene-disrupted mice revealed that male mice were defective in spermatogenesis and were infertile. DNA double strand-breaks persisted throughout meiosis and crossing-over failed in SETX mutant mice. These changes can be explained by the accumulation of R-loops, which interfere with Holiday junctions and crossing-over. We also showed that senataxin was localized to the XY body in pachytene cells and was involved in transcriptional silencing of these chromosomes. While the defect in meiotic recombination was striking in these animals, there was no evidence of neurodegeneration as observed in AOA2 patients. We discuss here potentially different roles for senataxin in proliferating and post-mitotic cells.

No MeSH data available.


Related in: MedlinePlus