mTORC1 controls the adaptive transition of quiescent stem cells from G0 to G(Alert).

A unique property of many adult stem cells is their ability to exist in a non-cycling, quiescent state. Although quiescence serves an essential role in preserving stem cell function until the stem cell is needed in tissue homeostasis or repair, defects in quiescence can lead to an impairment in tissue function. The extent to which stem cells can regulate quiescence is unknown. Here we show that the stem cell quiescent state is composed of two distinct functional phases, G0 and an 'alert' phase we term G(Alert). Stem cells actively and reversibly transition between these phases in response to injury-induced systemic signals. Using genetic mouse models specific to muscle stem cells (or satellite cells), we show that mTORC1 activity is necessary and sufficient for the transition of satellite cells from G0 into G(Alert) and that signalling through the HGF receptor cMet is also necessary. We also identify G0-to-G(Alert) transitions in several populations of quiescent stem cells. Quiescent stem cells that transition into G(Alert) possess enhanced tissue regenerative function. We propose that the transition of quiescent stem cells into G(Alert) functions as an 'alerting' mechanism, an adaptive response that positions stem cells to respond rapidly under conditions of injury and stress, priming them for cell cycle entry.

Sex differences and the interaction of age and sleep issues in neuropsychological testing performance across the lifespan in an ADD/ADHD sample from the years 1989 to 2009.

Chart review of population (9 to 80 years) neuropsychological test battery for ADHD diagnosis, questionnaires with multiple responders were evaluated in outpatient setting from 1989-2009. The focus was gender differences across age, diagnostic group (ADHD-Inattentive/ADHD plus), neuropsychological test performance, and reported sleep symptoms over the lifespan. Individuals were assigned to ADHD-I group or ADHD plus group (based upon secondary diagnosis of sleep, behavioral, emotional disturbance); ADHD not primary was excluded (brain insult, psychosis). Among these were 1,828 children (ages 9 to 14), adolescents (ages 15 to 17), and adults (ages 18 and above); 446 children (312 diagnosed ADHD-I), 218 adolescents (163 diagnosed ADHD-I), and 1,163 adults (877 ADHD-I). Sleep was problematic regardless of age, ADHD subtype, and gender. The type and number of sleep problems and fatigue were age dependent. ADHD subtype, gender, fatigue, age, and sleep (sleep onset, unrefreshing sleep, sleep maintenance) were significant variables affecting neuropsychological test performance (sequencing, cognitive flexibility, slow- and fast-paced input, divided attention, whole brain functioning). Findings suggest that ADHD involves numerous factors and symptoms beyond attention, such as sleep which interacts differently dependent upon age.

Genetic correction of splice site mutation in purified and enriched myoblasts isolated from mdx5cv mice.

BACKGROUND: Duchenne Muscular Dystrophy (DMD) is an X-linked genetic disorder that results in the production of a dysfunctional form of the protein, dystrophin. The mdx5cv mouse is a model of DMD in which a point mutation in exon 10 of the dystrophin gene creates an artificial splice site. As a result, a 53 base pair deletion of exon 10 occurs with a coincident creation of a frameshift and a premature stop codon. Using primary myoblasts from mdx5cv mice, single-stranded DNA oligonucleotides were designed to correct this DNA mutation. RESULTS: Single-stranded DNA oligonucleotides that were designed to repair this splice site mutation corrected the mutation in the gene and restored expression of wild-type dystrophin. This repair was validated at the DNA, RNA and protein level. We also report that the frequency of genetic repair of the mdx mutation can be enhanced if RNAi is used to suppress expression of the recombinase inhibitor protein Msh2 in cultures containing myoblasts but not in those heavily enriched in myoblasts. CONCLUSION: Exogenous manipulations, such as RNAi, are certainly feasible and possibly required to increase the successful application of gene repair in some primary or progenitor muscle cells.

Multiple roles for MSH2 in the repair of a deletion mutation directed by modified single-stranded oligonucleotides.

The mechanism by which modified single-stranded oligonucleotides (MSSOs) direct base changes in genes is not completely understood, but there is evidence that DNA damage, repair and cell cycle checkpoint proteins are involved in the targeted nucleotide exchange (TNE) process. We are interested in the role of the mismatch repair protein, Msh2 in the correction of a frameshift mutation in both yeast and mammalian cells. We show that this protein exerts different and opposing influences on the TNE reaction in MSH2 deficient yeast compared to MSH2(-/-) mammalian cells and in wild-type cells that have RNAi silenced Msh2. Data from yeast show a 10-fold decrease in the targeting frequency whereas mammalian cells have an elevated correction frequency. These results show that in yeast this protein is required for efficient targeting and may play a role in mismatch recognition and repair. In mammalian cells, Msh2 plays a suppressive role in TNE reaction by either precluding the oligonucleotide annealing to the target gene or by maintenance of a cell cycle checkpoint induced by the MSSO itself. These results reveal that the mechanism of TNE between yeast and mammalian cells is not conserved, and demonstrate that the suppression of the TNE reaction can be bypassed using RNAi against MSH2 designed to knockdown its expression.

Genetic re-engineering of Saccharomyces cerevisiae RAD51 leads to a significant increase in the frequency of gene repair in vivo.

Oligonucleotides can be used to direct the alteration of single nucleotides in chromosomal genes in yeast. Rad51 protein appears to play a central role in catalyzing the reaction, most likely through its DNA pairing function. Here, we re-engineer the RAD51 gene in order to produce proteins bearing altered levels of known activities. Overexpression of wild-type ScRAD51 elevates the correction of an integrated, mutant hygromycin resistance gene approximately 3-fold. Overexpression of an altered RAD51 gene, which encodes a protein that has a higher affinity for ScRad54, enhances the targeting frequency nearly 100-fold. Another mutation which increases the affinity of Rad51 for DNA was also found to increase gene repair when overexpressed in the cell. Other mutations in the Rad51 protein, such as one that reduces interaction with Rad52, has little or no effect on the frequency of gene repair. These data provide the first evidence that the Rad51 protein can be modified so as to increase the frequency of gene repair in yeast.

Enhancement of in vivo targeted nucleotide exchange by nonspecific carrier DNA.

Targeted nucleotide exchange (TNE) is a process in which an oligonucleotide bearing sequence complementarity aligns with the sequence of a target gene and directs the alteration of a single base. This technique can be used to repair a point mutation or mediate site-specific mutagenesis. A critical factor in the development of this approach centers around the elevation and stabilization of the frequencies with which these events occur. Here we describe a protocol for increasing the frequency of TNE in the true yeast, Saccharomyces cerevisiae, through the use of nonspecific, carrier oligonucleotides. These molecules, when added to the reaction, increase the TNE frequency up to 25-fold in some cases, perhaps by providing a molecular trap to bind factors, which may inactivate the specific targeting oligos.

Assessment of disease activity in muscular dystrophies by noninvasive imaging.

Muscular dystrophies are a class of disorders that cause progressive muscle wasting. A major hurdle for discovering treatments for the muscular dystrophies is a lack of reliable assays to monitor disease progression in animal models. We have developed a novel mouse model to assess disease activity noninvasively in mice with muscular dystrophies. These mice express an inducible luciferase reporter gene in muscle stem cells. In dystrophic mice, muscle stem cells activate and proliferate in response to muscle degeneration, resulting in an increase in the level of luciferase expression, which can be monitored by noninvasive, bioluminescence imaging. We applied this noninvasive imaging to assess disease activity in a mouse model of the human disease limb girdle muscular dystrophy 2B (LGMD2B), caused by a mutation in the dysferlin gene. We monitored the natural history and disease progression in these dysferlin-deficient mice up to 18 months of age and were able to detect disease activity prior to the appearance of any overt disease manifestation by histopathological analyses. Disease activity was reflected by changes in luciferase activity over time, and disease burden was reflected by cumulative luciferase activity, which paralleled disease progression as determined by histopathological analysis. The ability to monitor disease activity noninvasively in mouse models of muscular dystrophy will be invaluable for the assessment of disease progression and the effectiveness of therapeutic interventions.