Ensuring Mobility-Supporting Environments for an Aging Population: Critical Actors and Collaborations

Successful aging takes on an array of attributes, including optimal health and community participation. Research indicates that (1) persons with disabilities, including age-related disabilities, report frequent barriers to community participation, including unsuitable building design (43%), transportation (32%), and sidewalks/curbs (31%), and (2) many seniors report an inability to cross roads safely near their homes. This paper attempts to define mobility-related elements that contribute to optimal health and quality of life, within the context of successful aging. It then examines the impacts of community design on individual mobility, delving into which traditional and nontraditional actors—including architects, urban planners, transportation engineers, occupational therapists, and housing authorities—play critical roles in ensuring that community environments serve as facilitators (rather than barriers) to mobility. As America ages, mobility challenges for seniors will only increase unless both traditional aging specialists and many nontraditional actors make a concerted effort to address the challenges

DNA replication stress restricts ribosomal DNA copy number

Ribosomal RNAs (rRNAs) in budding yeast are encoded by ~100–200 repeats of a 9.1kb sequence arranged in tandem on chromosome XII, the ribosomal DNA (rDNA) locus. Copy number of rDNA repeat units in eukaryotic cells is maintained far in excess of the requirement for ribosome biogenesis. Despite the importance of the repeats for both ribosomal and non-ribosomal functions, it is currently not known how “normal” copy number is determined or maintained. To identify essential genes involved in the maintenance of rDNA copy number, we developed a droplet digital PCR based assay to measure rDNA copy number in yeast and used it to screen a yeast conditional temperature-sensitive mutant collection of essential genes. Our screen revealed that low rDNA copy number is associated with compromised DNA replication. Further, subculturing yeast under two separate conditions of DNA replication stress selected for a contraction of the rDNA array independent of the replication fork blocking protein, Fob1. Interestingly, cells with a contracted array grew better than their counterparts with normal copy number under conditions of DNA replication stress. Our data indicate that DNA replication stresses select for a smaller rDNA array. We speculate that this liberates scarce replication factors for use by the rest of the genome, which in turn helps cells complete DNA replication and continue to propagate. Interestingly, tumors from mini chromosome maintenance 2 (MCM2)-deficient mice also show a loss of rDNA repeats. Our data suggest that a reduction in rDNA copy number may indicate a history of DNA replication stress, and that rDNA array size could serve as a diagnostic marker for replication stress. Taken together, these data begin to suggest the selective pressures that combine to yield a “normal” rDNA copy number

Mcm2 hypomorph leads to acute leukemia or hematopoietic stem cell failure, dependent on genetic context

Minichromosome maintenance proteins (Mcm2-7) form a hexameric complex that unwinds DNA ahead of a replicative fork. The deficiency of Mcm proteins leads to replicative stress and consequent genomic instability. Mice with a germline insertion of a Cre cassette into the 3'UTR of the Mcm2 gene (designated Mcm2Cre ) have decreased Mcm2 expression and invariably develop precursor T-cell lymphoblastic leukemia/lymphoma (pre-T LBL), due to 100-1000 kb deletions involving important tumor suppressor genes. To determine whether mice that were protected from pre-T LBL would develop non-T-cell malignancies, we used two approaches. Mice engrafted with Mcm2Cre/Cre Lin- Sca-1+ Kit+ hematopoietic stem/progenitor cells did not develop hematologic malignancy; however, these mice died of hematopoietic stem cell failure by 6 months of age. Placing the Mcm2Cre allele onto an athymic nu/nu background completely prevented pre-T LBL and extended survival of these mice three-fold (median 296.5 vs. 80.5 days). Ultimately, most Mcm2Cre/Cre ;nu/nu mice developed B-cell precursor acute lymphoblastic leukemia (BCP-ALL). We identified recurrent deletions of 100-1000 kb that involved genes known or suspected to be involved in BCP-ALL, including Pax5, Nf1, Ikzf3, and Bcor. Moreover, whole-exome sequencing identified recurrent mutations of genes known to be involved in BCP-ALL progression, such as Jak1/Jak3, Ptpn11, and Kras. These findings demonstrate that an Mcm2Cre/Cre hypomorph can induce hematopoietic dysfunction via hematopoietic stem cell failure as well as a "deletor" phenotype affecting known or suspected tumor suppressor genes

Typha (Cattail) Invasion in North American Wetlands: Biology, Regional Problems, Impacts, Ecosystem Services, and Management

Typha is an iconic wetland plant found worldwide. Hybridization and anthropogenic disturbances have resulted in large increases in Typha abundance in wetland ecosystems throughout North America at a cost to native floral and faunal biodiversity. As demonstrated by three regional case studies, Typha is capable of rapidly colonizing habitats and forming monodominant vegetation stands due to traits such as robust size, rapid growth rate, and rhizomatic expansion. Increased nutrient inputs into wetlands and altered hydrologic regimes are among the principal anthropogenic drivers of Typha invasion. Typha is associated with a wide range of negative ecological impacts to wetland and agricultural systems, but also is linked with a variety of ecosystem services such as bioremediation and provisioning of biomass, as well as an assortment of traditional cultural uses. Numerous physical, chemical, and hydrologic control methods are used to manage invasive Typha, but results are inconsistent and multiple methods and repeated treatments often are required. While this review focuses on invasive Typha in North America, the literature cited comes from research on Typha and other invasive species from around the world. As such, many of the underlying concepts in this review are relevant to invasive species in other wetland ecosystems worldwide

Exploring Demographic, Physical, and Historical Explanations for the Genetic Structure of Two Lineages of Greater Antillean Bats

Observed patterns of genetic structure result from the interactions of demographic, physical, and historical influences on gene flow. The particular strength of various factors in governing gene flow, however, may differ between species in biologically relevant ways. We investigated the role of demographic factors (population size and sex-biased dispersal) and physical features (geographic distance, island size and climatological winds) on patterns of genetic structure and gene flow for two lineages of Greater Antillean bats. We used microsatellite genetic data to estimate demographic characteristics, infer population genetic structure, and estimate gene flow among island populations of Erophylla sezekorni/E. bombifrons and Macrotus waterhousii (Chiroptera: Phyllostomidae). Using a landscape genetics approach, we asked if geographic distance, island size, or climatological winds mediate historical gene flow in this system. Samples from 13 islands spanning Erophylla's range clustered into five genetically distinct populations. Samples of M. waterhousii from eight islands represented eight genetically distinct populations. While we found evidence that a majority of historical gene flow between genetic populations was asymmetric for both lineages, we were not able to entirely rule out incomplete lineage sorting in generating this pattern. We found no evidence of contemporary gene flow except between two genetic populations of Erophylla. Both lineages exhibited significant isolation by geographic distance. Patterns of genetic structure and gene flow, however, were not explained by differences in relative effective population sizes, island area, sex-biased dispersal (tested only for Erophylla), or surface-level climatological winds. Gene flow among islands appears to be highly restricted, particularly for M. waterhousii, and we suggest that this species deserves increased taxonomic attention and conservation concern

Screen for essential genes that maintain rDNA copy number.

<p>(A) Distribution of rDNA copy number across the yeast ts mutant collection. 175 and 113 strains had significantly lower (<70 copies) and higher copy number (>119 copies) respectively (p<0.05). (B) -log₁₀ transformed FDR q-values for significantly enriched (p<0.001) GO terms (sorted in order of increasing p-values from top to bottom) in low copy number hits.</p

Low rDNA copy number confers advantage under DNA replication stress.

<p>(A) 3 independent isolates each with normal or low rDNA copy number were generated by subcultuing wild-type or <i>fob1Δ GAL-POL1</i> cells in medium containing high or low galactose (high or low levels of Pol1 respectively) for ~50–75 generations (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007006#pgen.1007006.s006" target="_blank">S2 Table</a>) and 5-fold serial dilutions spotted on to medium with DNA replication stress (low Pol1). (B) 10-fold serial dilutions of wild-type and <i>fob1Δ</i> cells (~200–250 rDNA copies) along with cells having 20–110 rDNA copies [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007006#pgen.1007006.ref003" target="_blank">3</a>] were spotted on medium containing hydroxyurea (HU). rDNA copy number was confirmed by ddPCR. Error bars represent standard deviation for each individual reaction.</p

Design and validation of a ddPCR assay for rDNA copy number measurement.

<p>(A) Targets (red bars) within the rDNA and single copy reference (<i>TUB1</i>) loci in yeast. (B) rDNA copy number in 3 independent isolates each of 2 different wild-type laboratory yeast strains, BY4741 and W303, and 4 isogenic strains with varying rDNA copy number generated by Ide et al. [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007006#pgen.1007006.ref003" target="_blank">3</a>]. (C) rDNA copy number in 8 technical replicates each of BY4741 and W303. (D) rDNA copy number in 3 independent isolates each of mutants with expanded rDNA arrays. Error bars represent standard deviation for each individual reaction.</p

Contraction of the rDNA array promotes timely completion of DNA replication and cell cycle progression.

<p>Wild-type <i>GAL-POL1</i> cells were subcultured in medium containing high or low levels of galactose for ~75 generations to generate 3 independent isolates each with normal or low rDNA copy number (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007006#pgen.1007006.s006" target="_blank">S2 Table</a>). (A) Representative DNA content profiles over time are shown for asynchronous cultures of isolates with normal (i) and low (ii) rDNA copy number following inoculation into the indicated medium which determines high or low levels of DNA polymerase α. (B) Fraction of cells in S-phase in each of the 4 conditions in (A). Error bars indicate standard deviation based on 3 independent isolates. Statistical significance of differences between fraction of cells in S-phase in high and low levels of DNA polymerase α was calculated using a standard 2-tailed t-test. *—p<0.05, ****—p<0.0001. (C) Increased rARS firing in nicotinamide exacerbates growth defects under conditions of DNA replication stress.</p