North and South America were the last continents to be explored and settled by modern humans at the end of the Pleistocene. Genetic data, derived from contemporary populations and ancient ...individuals, show that the first Americans originated from Asia and after several population splits moved south of the continental ice sheets that covered Canada sometime between ~17.5 and ~14.6 thousand years (ka) ago. Archaeological evidence shows that geographically dispersed populations lived successfully, using biface, blade, and osseous technologies, in multiple places in North and South America between ~15.5 and ~14 ka ago. Regional archaeological complexes emerged by at least ~13 ka ago in North America and ~12.9 ka ago in South America. Current genetic and archaeological data do not support an earlier (pre-17.5 ka ago) occupation of the Americas.
Small heat shock proteins are a diverse, ancient, and important family of proteins. All organisms possess small heat shock proteins (sHSPs), indicating that these proteins evolved very early in the ...history of life prior to the divergence of the three domains of life (Archaea, Bacteria, and Eukarya). Comparing the structures of sHSPs from diverse organisms across these three domains reveals that despite considerable amino acid divergence, many structural features are conserved. Comparisons of the sHSPs from diverse organisms reveal conserved structural features including an oligomeric form with a β-sandwich that forms a hollow ball. This conservation occurs despite significant divergence in primary sequences. It is well established that sHSPs are molecular chaperones that prevent misfolding and irreversible aggregation of their client proteins. Most notably, the sHSPs are extremely diverse and variable in plants. Some plants have >30 individual sHSPs. Land plants, unlike other groups, possess distinct sHSP subfamilies. Most are highly up-regulated in response to heat and other stressors. Others are selectively expressed in seeds and pollen, and a few are constitutively expressed. As a family, sHSPs have a clear role in thermotolerance, but attributing specific effects to individual proteins has proved challenging. Considerable progress has been made during the last 15 years in understanding the sHSPs. However, answers to many important questions remain elusive, suggesting that the next 15 years will be at least equally rewarding.
Small heat shock proteins (sHSPs) are an ubiquitous protein family found in archaea, bacteria and eukaryotes. In plants, as in other organisms, sHSPs are upregulated by stress and are proposed to act ...as molecular chaperones to protect other proteins from stress-induced damage. sHSPs share an ‘α-crystallin domain’ with a β-sandwich structure and a diverse N-terminal domain. Although sHSPs are 12–25 kDa polypeptides, most assemble into oligomers with ≥ 12 subunits. Plant sHSPs are particularly diverse and numerous; some species have as many as 40 sHSPs. In angiosperms this diversity comprises ≥ 11 sHSP classes encoding proteins targeted to the cytosol, nucleus, endoplasmic reticulum, chloroplasts, mitochondria and peroxisomes. The sHSPs underwent a lineage-specific gene expansion, diversifying early in land plant evolution, potentially in response to stress in the terrestrial environment, and expanded again in seed plants and again in angiosperms. Understanding the structure and evolution of plant sHSPs has progressed, and a model for their chaperone activity has been proposed. However, how the chaperone model applies to diverse sHSPs and what processes sHSPs protect are far from understood. As more plant genomes and transcriptomes become available, it will be possible to explore theories of the evolutionary pressures driving sHSP diversification.
The olfactory bulbectomized rodent has long been one of the preferred animal models of depression and certain other neuropsychiatric diseases. In fact, it is considered unparalleled, by some, in the ...search for antidepressant medication and the literature generated about the model is prodigious. We have revisited the “syndrome” of behavioral sequela following bulbectomy choosing ecologically valid tests likely to be underpinned with evolutionarily preserved neural circuits. Our test battery included measurements of activity, intermale aggression, pleasure seeking, stress/fear and non-spatial memory. The emphasis was on the timetable of syndrome emergence, since this has been understudied and bears on the widely held belief that non-olfactory effects dominate. Our results largely agree with previous reports describing the behavioral syndrome in that we document bulbectomized mice as hyperactive, non-aggressive and fearless. However, we did not find deficits in memory as have frequently been reported in previous studies. Notably, our results revealed that some syndrome behaviors—including the hallmark of hyperactivity—appear immediately or soon after surgery. This rapid appearance casts doubt on the widely held view that compensatory reorganization of limbic and prefrontal cortical areas following bulbectomy underlies the syndrome. Rather, hyperactivity, non-aggressiveness, reduced fear and diminished sucrose preference in the olfactory bulbectomized mouse find ready explanations in the loss of smell that is the immediate and irreversible outcome of bulbectomy. Finally, after a critical consideration of the literature and our results, we conclude that the olfactory bulbectomy model lacks the validity and simplicity previously credited to it. Indeed, we deem this lesion unsuitable as a model of most neuropsychiatric diseases since its effects are at least as complex and misunderstood as the disorders it is purported to model.
A search is ongoing for compressed gas insulants of comparable performance with sulphur hexafluoride, which will avoid its severe global warming potential. This work will be assisted by a generic ...understanding of the factors that limit the high voltage withstanding strength of compressed gases. Most available experimental data relate to high-pressure SF6 breakdown, but no quantitative physical model for breakdown voltage prediction has been developed other than empirical algorithms. The paper shows that a new form of the classical Paschen law can account for these data, which will provide a useful guide for the economical testing of candidate insulants and for the general design and physical limitations of equipment using compressed gases. The paper also examines the transient changes in compressible gas density that arise from shock wave development, which may influence high-pressure breakdown and determine the breakdown voltage.
When did humans colonize the Americas? From where did they come and what routes did they take? These questions have gripped scientists for decades, but until recently answers have proven difficult to ...find. Current genetic evidence implies dispersal from a single Siberian population toward the Bering Land Bridge no earlier than about 30,000 years ago (and possibly after 22,000 years ago), then migration from Beringia to the Americas sometime after 16,500 years ago. The archaeological records of Siberia and Beringia generally support these findings, as do archaeological sites in North and South America dating to as early as 15,000 years ago. If this is the time of colonization, geological data from western Canada suggest that humans dispersed along the recently deglaciated Pacific coastline.
One-third of all protein-coding genes from bacterial genomes cannot be annotated with a function. Here, to investigate the functions of these genes, we present genome-wide mutant fitness data from 32 ...diverse bacteria across dozens of growth conditions. We identified mutant phenotypes for 11,779 protein-coding genes that had not been annotated with a specific function. Many genes could be associated with a specific condition because the gene affected fitness only in that condition, or with another gene in the same bacterium because they had similar mutant phenotypes. Of the poorly annotated genes, 2,316 had associations that have high confidence because they are conserved in other bacteria. By combining these conserved associations with comparative genomics, we identified putative DNA repair proteins; in addition, we propose specific functions for poorly annotated enzymes and transporters and for uncharacterized protein families. Our study demonstrates the scalability of microbial genetics and its utility for improving gene annotations.
The only certain evidence for prehistoric human hunting of horse and camel in North America occurs at the Wally’s Beach site, Canada. Here, the butchered remains of seven horses and one camel are ...associated with 29 nondiagnostic lithic artifacts. Twenty-seven new radiocarbon ages on the bones of these animals revise the age of these kill and butchering localities to 13,300 calibrated y B.P. The tight chronological clustering of the eight kill localities at Wally’s Beach indicates these animals were killed over a short period. Human hunting of horse and camel in Canada, coupled with mammoth, mastodon, sloth, and gomphothere hunting documented at other sites from 14,800–12,700 calibrated y B.P., show that 6 of the 36 genera of megafauna that went extinct by approximately 12,700 calibrated y B.P. were hunted by humans. This study shows the importance of accurate geochronology, without which significant discoveries will go unrecognized and the empirical data used to build models explaining the peopling of the Americas and Pleistocene extinctions will be in error.
Significance Archaeological discoveries at Wally’s Beach, Canada, provide the only direct evidence of horse and camel hunting in the Americas at the end of the last Ice Age. Here, seven horses and one camel were attacked and butchered near a river crossing by prehistoric hunters. New radiocarbon dates revise the age of these kill and butchering localities to 13,300 y ago. Other North American kill and butchering sites show that prehistoric hunters preyed on 6 of the 36 genera of large mammals, called megafauna, for at least 2,000 y before these animals became extinct, around 12,700 y ago. Accurate dating is necessary to build meaningful chronologies for the Ice Age peopling of the Americas and to understand megafauna extinctions.
The Clovis complex is considered to be the oldest unequivocal evidence of humans in the Americas, dating between 11,500 and 10,900 radiocarbon years before the present (¹⁴C yr B.P.). Adjusted ¹⁴C ...dates and a reevaluation of the existing Clovis date record revise the Clovis time range to 11,050 to 10,800 ¹⁴C yr B.P. In as few as 200 calendar years, Clovis technology originated and spread throughout North America. The revised age range for Clovis overlaps non-Clovis sites in North and South America. This and other evidence imply that humans already lived in the Americas before Clovis.
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