Compromised genomic integrity impedes muscle growth after Atrx inactivation

Abstract

ATR-X syndrome is a severe intellectual disability disorder caused by mutations in the ATRX gene. Many ancillary clinical features are attributed to CNS deficiencies, yet most patients have muscle hypotonia, delayed ambulation, or kyphosis, pointing to an underlying skeletal muscle defect. Here, we identified a cell-intrinsic requirement for Atrx in postnatal muscle growth and regeneration in mice. Mice with skeletal muscle-specific Atrx conditional knockout (Atrx cKO mice) were viable, but by 3 weeks of age presented hallmarks of underdeveloped musculature, including kyphosis, 20% reduction in body mass, and 34% reduction in muscle fiber caliber. Atrx cKO mice also demonstrated a marked regeneration deficit that was not due to fewer resident satellite cells or their inability to terminally differentiate. However, activation of Atrx-null satellite cells from isolated muscle fibers resulted in a 9-fold reduction in myoblast expansion, caused by delayed progression through mid to late S phase. While in S phase, Atrx colocalized specifically to late-replicating chromatin, and its loss resulted in rampant signs of genomic instability. These observations support a model in which Atrx maintains chromatin integrity during the rapid developmental growth of a tissue.

Alpha Thalassemia/Mental Retardation Syndrome X-linked Gene Product ATRX Is Required for Proper Replication Restart and Cellular Resistance to Replication Stress

“…The slower progression through S phase and delayed mitotic entry observed in ATRX-deficient cells could be due to stalled replication forks in the absence of ATRX. Indeed, a recent study showed a similar observation on the delayed S-phase progression upon ATRX inactivation (37). These replication defects in ATRX deficient cells may lead to reduced number of replication forks in these cells, and therefore indirectly affect Chk1 activation in response to HU, as we observed in this study.…”

The Polycomb Repressive Complex 1 Protein BMI1 Is Required for Constitutive Heterochromatin Formation and Silencing in Mammalian Somatic Cells

“…It is thus notable that Bmi1-deficient mice show reduced lifespan, genomic instability, neurodegeneration, and progeria features (38,(42)(43)(44)(45)75). Similar anomalies were also reported for ATRxdeficient mice (18,20). Taken together, this raises the possibility that BMI1 requirement for constitutive heterochromatin formation and silencing could underlie the premature aging/ senescence and genomic instability phenotypes observed in Bmi1-null mice and cells.…”

MYCN Amplification and ATRX Mutations are Incompatible in Neuroblastoma

“…Mice were genotyped using the published protocols [2][3][4][5] . Mice with the desired genotypes were enrolled in the study at the time of weaning and were followed up by abdominal palpation at least once every 2 weeks starting from age of 6 weeks.…”

“…MYCN amplification and age at diagnosis are the two most powerful predictors of outcome, with survival rates 5 to 10 times higher in infants than in adolescents or young adults (AYAs) [1][2][3][4] . Although MYCN amplification is equally distributed across age groups, previous genomic analyses of stage 4 pediatric neuroblastoma samples identified the ATRX mutations in 44% of AYAs (>12 y), 17% of children (18 mo-12 y), and 0% of infants (<18 mo) 1,5 .…”