Genetic variation in ecophysiological and survival responses to drought in two native grasses: Koeleria macrantha and Elymus elymoides

Genetic variation in ecophysiological and survival responses to drought was studied in 2 northern Arizona native grass species, Koeleria macrantha (Ledeb.) Schult. (prairie Junegrass) and Elymus elymoides (Raf.) Swezey. ssp. elymoides (squirreltail). Low- and high-elevation populations of each species were compared in a greenhouse common garden experiment that included simulated drought. Leaf gas-exchange characteristics were significantly affected by simulated drought and often by population elevation, but gas-exchange responses to drought were similar for high- and low-elevation populations. Compared to high-elevation populations, low-elevation populations of both species had higher net photosynthetic rate and predawn water potential, and for E. elymoides had higher stomatal conductance. Leaf-level water-use efficiency did not differ between populations for either species. Populations also differed significantly in leaf morphological characteristics related to water use. Compared to high-elevation populations, low-elevation populations of both species had smaller leaves. Low-elevation populations of both species survived aboveground longer than high-elevation populations during drought, with a larger difference in K. macrantha than in E. elymoides. These results suggest strong selection for drought adaptation and water use along an elevational and water-availability gradient in native grasses. Se estudió la variación genética en respuestas ecofisiológica y de sobrevivencia a la sequía en dos especies de pasto nativo del norte de Arizona, Koeleria macrantha (Ledeb.) Schult. (“prairie Junegrass”) y Elymus elymoides (Raf.) Swezey. spp. elymoides (“squirreltail”). Se compararon poblaciones de cada especie a elevaciones altas y bajas durante un experimento de jardín común en un invernadero que simulaba condiciones de sequía. Las características relacionadas con el intercambio de gases a nivel de hoja se vieron afectadas significativamente por la sequía simulada y con frecuencia por la elevación de la población, pero la respuesta del intercambio de gases a la sequía fue similar en las poblaciones de alta y baja elevación. En comparación con las poblaciones altas, las poblaciones bajas, en ambas especies, tuvieron una elevada tasa neta de fotosíntesis y un mayor potencial hídrico previo al amanecer; E. elymoides tuvo mayor conductancia estomática. La eficiencia en el uso del agua (EUA) a nivel de hoja no difirió entre poblaciones en ninguna especie. Las poblaciones sí difirieron significativamente en las características de la morfología de la hoja relacionadas con el uso del agua. Comparadas con las poblaciones altas, las poblaciones bajas de ambas especies tuvieron hojas más pequeñas. Durante la sequía, la parte de la planta que estaba encima de la tierra sobrevivió por más tiempo en las poblaciones bajas de ambas especies que en las poblaciones altas, con una mayor diferencia en K. macrantha que en E. elymoides. Estos resultados indican que hay una fuerte selección para la adaptación a la sequía y el uso del agua a lo largo de una gradiente de elevación y de disponibilidad de agua en pastos nativos.     

A sequence-based variation map of 8.27 million SNPs in inbred mouse strains

A dense map of genetic variation in the laboratory mouse genome will provide insights into the evolutionary history of the species and lead to an improved understanding of the relationship between inter-strain genotypic and phenotypic differences. Here we resequence the genomes of four wild-derived and eleven classical strains. We identify 8.27 million high-quality single nucleotide polymorphisms (SNPs) densely distributed across the genome, and determine the locations of the high (divergent subspecies ancestry) and low (common subspecies ancestry) SNP-rate intervals for every pairwise combination of classical strains. Using these data, we generate a genome-wide haplotype map containing 40,898 segments, each with an average of three distinct ancestral haplotypes. For the haplotypes in the classical strains that are unequivocally assigned ancestry, the genetic contributions of the Mus musculus subspecies--M. m. domesticus, M. m. musculus, M. m. castaneus and the hybrid M. m. molossinus--are 68%, 6%, 3% and 10%, respectively; the remaining 13% of haplotypes are of unknown ancestral origin. The considerable regional redundancy of the SNP data will facilitate imputation of the majority of these genotypes in less-densely typed classical inbred strains to provide a complete view of variation in additional strains.     

ATM stabilizes DNA double-strand-break complexes during V(D)J recombination

The ATM (ataxia-telangiectasia mutated) protein kinase mediates early cellular responses to DNA double-strand breaks (DSBs) generated during metabolic processes or by DNA-damaging agents. ATM deficiency leads to ataxia-telangiectasia, a disease marked by lymphopenia, genomic instability and an increased predisposition to lymphoid malignancies with chromosomal translocations involving lymphocyte antigen receptor loci. ATM activates cell-cycle checkpoints and can induce apoptosis in response to DNA DSBs. However, defects in these pathways of the DNA damage response cannot fully account for the phenotypes of ATM deficiency. Here, we show that ATM also functions directly in the repair of chromosomal DNA DSBs by maintaining DNA ends in repair complexes generated during lymphocyte antigen receptor gene assembly. When coupled with the cell-cycle checkpoint and pro-apoptotic activities of ATM, these findings provide a molecular explanation for the increase in lymphoid tumours with translocations involving antigen receptor loci associated with ataxia-telangiectasia.     

Temporal and spatial distribution of highway mortality of mule deer on newly constructed roads at Jordanelle Reservoir, Utah

In this paper we evaluated traffic characteristics and vegetation and topographic features associated with mule deer kills on 3 highways (US 40, SR 32, SR 248) in northeastern Utah. We also compared number, and sex and age composition of roadkills to that of the living population observed during spotlight counts. From 15 October 1991 to 14 October 1993 we documented 397 deer roadkills: 51.6% were does, 18.9% bucks, 21.7% fawns, and 7.8% could not be classified. Sixty-seven percent of adult kills were 2.5 yr of age. Kill composition compared closely to spotlight counts. Of 1515 spotlight deer, 65.2% were does, 8.9% bucks, and 25.9% fawns. Spotlight density and deer mortality were strongly correlated from summer 1992 through summer 1993 ( r = 0.94). Traffic conditions, topographic features, and vegetative characteristics contributed to mortality levels. Roadkills were highest along US 40 (68% year 1, 55% year 2) where traffic volume and speed were significantly higher along either state route. Large drainages intersected highways in 78% of designated kill zones. Roads adjacent to agricultural areas along all routes sustained the fewest highway mortalities. Percent cover was higher (40%) in kill zones than in other areas (29%).     

The ectodomain of Toll-like receptor 9 is cleaved to generate a functional receptor

Mammalian Toll-like receptors (TLRs) 3, 7, 8 and 9 initiate immune responses to infection by recognizing microbial nucleic acids; however, these responses come at the cost of potential autoimmunity owing to inappropriate recognition of self nucleic acids. The localization of TLR9 and TLR7 to intracellular compartments seems to have a role in facilitating responses to viral nucleic acids while maintaining tolerance to self nucleic acids, yet the cell biology regulating the transport and localization of these receptors remains poorly understood. Here we define the route by which TLR9 and TLR7 exit the endoplasmic reticulum and travel to endolysosomes in mouse macrophages and dendritic cells. The ectodomains of TLR9 and TLR7 are cleaved in the endolysosome, such that no full-length protein is detectable in the compartment where ligand is recognized. Notably, although both the full-length and cleaved forms of TLR9 are capable of binding ligand, only the processed form recruits MyD88 on activation, indicating that this truncated receptor, rather than the full-length form, is functional. Furthermore, conditions that prevent receptor proteolysis, including forced TLR9 surface localization, render the receptor non-functional. We propose that ectodomain cleavage represents a strategy to restrict receptor activation to endolysosomal compartments and prevent TLRs from responding to self nucleic acids.     

Temperature dependence of ventilation and O2-extraction in the Kittiwake,Rissa tridactyla

Summary At low ambient temperature the Kittiwake,Rissa tridactyla, increased its oxygen consumption, while lung ventilation remained unchanged. A changed breathing pattern (lower frequency and higher tidal volumes) and an increase in the lung O₂-extraction was responsible for the observed decrease in the ventilatory requirement, which may be important because it reduces the respiratory heat loss during cold exposure.The study was supported by the Danish Natural Science Research Council, Gads Fond, Tipsmidlerne and Norsk Polarinstitutt.     

A variant associated with nicotine dependence, lung cancer and peripheral arterial disease

Smoking is a leading cause of preventable death, causing about 5 million premature deaths worldwide each year. Evidence for genetic influence on smoking behaviour and nicotine dependence (ND) has prompted a search for susceptibility genes. Furthermore, assessing the impact of sequence variants on smoking-related diseases is important to public health. Smoking is the major risk factor for lung cancer (LC) and is one of the main risk factors for peripheral arterial disease (PAD). Here we identify a common variant in the nicotinic acetylcholine receptor gene cluster on chromosome 15q24 with an effect on smoking quantity, ND and the risk of two smoking-related diseases in populations of European descent. The variant has an effect on the number of cigarettes smoked per day in our sample of smokers. The same variant was associated with ND in a previous genome-wide association study that used low-quantity smokers as controls, and with a similar approach we observe a highly significant association with ND. A comparison of cases of LC and PAD with population controls each showed that the variant confers risk of LC and PAD. The findings provide a case study of a gene-environment interaction, highlighting the role of nicotine addiction in the pathology of other serious diseases.     

Gap junction adhesion is necessary for radial migration in the neocortex

Radial glia, the neuronal stem cells of the embryonic cerebral cortex, reside deep within the developing brain and extend radial fibres to the pial surface, along which embryonic neurons migrate to reach the cortical plate. Here we show that the gap junction subunits connexin 26 (Cx26) and connexin 43 (Cx43) are expressed at the contact points between radial fibres and migrating neurons, and acute downregulation of Cx26 or Cx43 impairs the migration of neurons to the cortical plate. Unexpectedly, gap junctions do not mediate neuronal migration by acting in the classical manner to provide an aqueous channel for cell-cell communication. Instead, gap junctions provide dynamic adhesive contacts that interact with the internal cytoskeleton to enable leading process stabilization along radial fibres as well as the subsequent translocation of the nucleus. These results indicate that gap junction adhesions are necessary for glial-guided neuronal migration, raising the possibility that the adhesive properties of gap junctions may have an important role in other physiological processes and diseases associated with gap junction function.