The Alternative Lengthening of Telomeres (ALT) pathway is a telomerase-independent pathway for telomere maintenance that is active in a significant subset of human cancers and in vitro immortalized cell lines. ALT is thought to involve templated extension of telomeres through homologous recombination, but the genetic or epigenetic changes that unleash ALT are not known. Recently, mutations in the ATRX/DAXX chromatin remodeling complex and histone H3.3 were found to correlate with features of ALT in pancreatic neuroendocrine cancers, pediatric glioblastomas, and other tumors of the central nervous system, suggesting that these mutations might contribute to the activation of the ALT pathway in these cancers. We have taken a comprehensive approach to deciphering ALT by applying genomic, molecular biological, and cell biological approaches to a panel of 22 ALT cell lines, including cell lines derived in vitro. Here we show that loss of ATRX protein and mutations in the ATRX gene are hallmarks of ALT–immortalized cell lines. In addition, ALT is associated with extensive genome rearrangements, marked micronucleation, defects in the G2/M checkpoint, and altered double-strand break (DSB) repair. These attributes will facilitate the diagnosis and treatment of ALT positive human cancers.

The microRNA miR-137 represses expression of Ezh2, a histone methyltransferase, which in turn alters the epigenetic architecture of chromatin that is important for regulation of miR-137 levels.

Fragile X syndrome (FXS), the most common form of inherited mental retardation, is caused by the loss of functional fragile X mental retardation protein (FMRP). FMRP is an RNA–binding protein that can regulate the translation of specific mRNAs. Adult neurogenesis, a process considered important for neuroplasticity and memory, is regulated at multiple molecular levels. In this study, we investigated whether Fmrp deficiency affects adult neurogenesis. We show that in a mouse model of fragile X syndrome, adult neurogenesis is indeed altered. The loss of Fmrp increases the proliferation and alters the fate specification of adult neural progenitor/stem cells (aNPCs). We demonstrate that Fmrp regulates the protein expression of several components critical for aNPC function, including CDK4 and GSK3β. Dysregulation of GSK3β led to reduced Wnt signaling pathway activity, which altered the expression of neurogenin1 and the fate specification of aNPCs. These data unveil a novel regulatory role for Fmrp and translational regulation in adult neurogenesis.

Small interfering RNAs (siRNAs) and microRNAs (miRNAs) are sequence-specific posttranscriptional regulators of gene expression. Although major components of the RNA interference (RNAi) pathway have been identified, regulatory mechanisms for this pathway remain largely unknown. Here we demonstrate that the RNAi pathway can be modulated intracellularly by small molecules. We have developed a cell-based assay to monitor the activity of the RNAi pathway and find that the small-molecule enoxacin (Penetrex) enhances siRNA-mediated mRNA degradation and promotes the biogenesis of endogenous miRNAs. We show that this RNAi-enhancing activity depends on the trans-activation-responsive region RNA-binding protein. Our results provide a proofof-principle demonstration that small molecules can be used to modulate the activity of the RNAi pathway. RNAi enhancers may be useful in the development of research tools and therapeutics.

Scleroderma renal crisis (SRC) is a rare, potentially life-threatening complication that affects 2-15% of patients with systemic sclerosis (SSc, also known as scleroderma). SRC typically presents in patients with early, rapidly progressive, diffuse cutaneous SSc within the first 3-5 years after the onset of a non-Raynaud sign or symptom. SRC is characterized by an acute, usually symptomatic increase in blood pressure, a rise in serum creatinine levels, oliguria and thrombotic microangiopathy in about 50% of patients. The prognosis of SRC substantially improved in the 1980s with the introduction of angiotensin-converting-enzyme inhibitors for rapid blood pressure control, with additional antihypertensive agents as required. However, the survival of patients with SRC can still be improved. Current patient survival is 70-82% at 1 year, but decreases to 50-60% at 5 years despite dialysis support. Patients with SRC who show no signs of renal functional recovery despite timely blood pressure control are candidates for transplantation. In this Review, we discuss progress made in the identification and proactive management of patients at risk of SRC and make recommendations aimed at optimizing management for those who progress to chronic kidney failure.