EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES
Characteristics of early Solar System asteroid
A piece of the EC 002 meteorite. Image credit: Maine Mineral and Gem Museum/Darryl Pitt.
The nature of the crusts of primordial, differentiated protoplanets, which are generated through partial melting in the depths of bodies that formed in the early Solar System, is largely unknown, mostly because of a scarcity of sample material. Jean-Alix Barrat et al. report that EC 002, meteoritic lava found in the Sahara in 2020, exhibits a crystallization age of 4.565 billion years ago, earlier than other known samples. The authors determined the age through analysis of aluminum and magnesium isotopes and report that the crustal sample likely crystallized from a partial melt of a noncarbonaceous material formed around 4.566 billion years ago. The silica-rich chemical composition classifies the rock as andesitic, which differs from the known crusts of other asteroids that are basaltic. However, the composition of the parent body of EC 002 was probably not atypical, suggesting that andesitic crusts may have been common in protoplanets forming in the early Solar System. According to the authors, no known asteroid shares the chemical composition of EC 002, suggesting that early protoplanets with andesitic crusts may have either been incorporated into planetary bodies or destroyed. — P.G.
PNAS e2026129118 (2021)
EVOLUTION
Classification of an ancient spore-producing tree
Type specimen of Paratingia wuhaia, a 298 million-year-old tree, revealing an ancient seed plant sister group.
Noeggerathiales is an order of plants that lived between 323 and 252 million years ago, and although much is known about the order’s structure and geographic range, a lack of preserved plant anatomy has prevented its classification into the evolutionary tree of life. Jun Wang et al. describe a noeggerathialean plant with complete anatomical preservation from a 298-million-year-old ash deposit, including anatomical details that enable its evolutionary classification. The plant species, Paratingia wuhaia, is a small woody tree, with a crown of leaves and fertile shoots that produce spores. Details of the plant’s anatomy suggest that it belongs to the progymnosperm lineage. Paratingia extends the known temporal range of progymnosperms by around 60 million years and demonstrates that the spore-producing progymnosperm lineage, which is a sister group to seed plants, continued to diversify in parallel with diversification of seed-producing plants and independently developed fertile organs similar to cones, as found in Paratingia. According to the authors, the continued diversification of progymnosperms for around 110 million years after divergence from seed-producing plants and the connection of Noeggerathiales to progymnosperms clarifies the significance of the order in the plant evolutionary record. — P.G.
PNAS e2013442118 (2021)
NEUROSCIENCE
Origin of potassium channels in Alzheimer’s disease
In the central nervous system, micro-glia and a small fraction of peripherally derived monocytes and macrophages (CNS-MPs) collectively mediate immune responses, including those associated with Alzheimer’s disease (AD). Although high expression levels of Kv1.3 potassium channels in CNS-MPs offer a promising therapeutic target, key molecular details as well as the cellular origin of Kv1.3-expressing CNS-MPs remain unclear. Supriya Ramesha, Sruti Rayaprolu, et al. used flow cytometry to detect functional cell-surface Kv1.3 channels in CNS-MPs from an amyloid beta (Aβ) AD mouse model and fresh, unfrozen human AD brain tissue. The analyses revealed that Kv1.3 expression in mice is restricted to a subset of microglia-derived cells and upregulated in an Aβ-dependent manner that likely reflects progressive Aβ accumulation. Furthermore, the studies showed that Kv1.3 expression in human AD brain tissue is similarly restricted to a subpopulation of CNS-MPs and, despite notable differences, expressed in patterns resembling the Aβ mouse model. The authors used a model of irradiation and bone marrow chimerism and found that Kv1.3-expressing CNS-MPs in mice originate from microglia. According to the authors, Kv1.3 inhibition reduces Aβ accumulation and skews the microglial population toward pro-phagocytic and protective phenotypes. — T.J.
PNAS e2013545118 (2021)
GENETICS
Identifying genetic determinants for HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP) in a Japanese population
The human T cell leukemia virus type 1 (HTLV-1) is responsible for T cell leukemia and HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease of the central nervous system. Marina Penova, Shuji Kawaguchi, et al. conducted a large-scale genome-wide association (GWA) study and comprehensive genotyping of classical HLA genes to identify genetic determinants of HAM/TSP onset in a Japanese population. They used DNA from 731 HAM/TSP patients and 846 asymptomatic HTLV-1 carriers for 126,394 single nucleotide polymorphism markers in the GWA study. In addition, the researchers genotyped HLA-A, -B, -C, -DPB1, -DQB1, and -DRB1 genes using next-generation sequencing in 651 HAM/TSP patients and 804 carriers. Analysis of amino acid residues in the groove domain (G-DOMAIN) of HLA proteins identified the amino acid position 7 in the G-BETA domain of HLA-DRB1 as being most significantly associated with HAM/TSP. Leucine at this position (DRB1-GB-7-Leu) was associated with increased susceptibility to HAM/TSP, with individuals homozygous for DRB1-GB-7-Leu having a ninefold associated increased risk of HAM/TSP, whereas proline at this position (DRB1-GB-7-Pro) was protective. These effects were found to be independent of the known risk associated with proviral load. The authors conclude that DRB1-GB-7-Leu is a genetic risk factor for HAM/TSP development independent of proviral load, and suggest that it could potentially be useful as a biomarker for HAM/TSP development risk. — S.R.
PNAS e2004199118 (2021)
ECOLOGY
Ecosystem responses to shifts in predator and prey behavior
A southern sea otter (Enhydra lutris nereis) foraging on a purple sea urchin (Strongylocentrotus purpuratus) in Monterey Bay, California. Image credit: Morgan Rector (photographer).
Ecosystems are subject to both predation-driven and resource-driven influences and processes that can facilitate community structure and functioning. Joshua Smith et al. studied the ecological implications of how climate, disease, and disturbance eroded the strength of predation-driven control in a marine ecosystem through changes in prey traits and predator behaviors. In 2014, in the kelp forests along the Pacific coast of North America, sea star wasting disease dramatically reduced the number of sunflower sea stars, predators of purple sea urchins, at around the same time that climatic stressors reduced the amount of kelp on which urchins graze. The resulting shift in behavior by the food-limited urchins to active foraging led to a patchy mosaic of kelp forests and urchin-grazed barrens, with urchins declining in energetically demanding gonad production. Sea otters then increased their urchin consumption, but the authors found that their predation was based not on prey density but on the distribution of urchins’ gonad condition and energetic profitability. The otters thus mostly ignored starved and energetically depleted urchins in barrens. According to the authors, the results suggest otter preference for the forest-based urchins enhanced kelp patch resistance to overgrazing, but because otters did not forage for urchins in the barrens, they did not enhance kelp recovery. — P.G.
PNAS e2012493118 (2021)
PSYCHOLOGICAL AND COGNITIVE SCIENCES
Passion and achievement in sociocultural contexts
Identifying the people most likely to achieve success is an ongoing challenge in every field. In Western societies, where independent models of motivation are prevalent, “passion,” which is quantified using measures of interest, enjoyment, and efficacy, is considered important for achievement, and less passion is often considered a sign of less potential. To examine how the link between passion and achievement varies with culture, Xingyu Li et al. analyzed three large-scale representative datasets of 1.2 million adolescent students in 59 societies around the world. Passion was positively tied to academic achievement in science, mathematics, and reading in all societies, but the link between passion and academic achievement was significantly moderated by a society’s level of individualism. In individualistic societies, passion correlated more strongly with achievement, was tied to a larger gain in achievement, and explained between-student variance in achievement to a greater extent, compared with collectivistic societies, where interdependent models of motivation are more prevalent. Parental emotional support mattered as much as passion in predicting performance in collectivistic cultures but did not predict achievement in individualistic cultures. According to the authors, systematic cultural variation exists in the relationship between passion and achievement, and over-emphasizing the role of passion in admission and employment decisions may risk passing over or mismanaging talented people. — S.R.
PNAS e2016964118 (2021)
EVOLUTION
Bird-like genome in a frog
P. ornatum. Image credit: Stephen Mahony (photographer).
Genome size varies across the tree of life, with frogs and birds possessing large and small genomes, respectively. The mechanisms by which genomes shrink are poorly understood. Sangeet Lamichhaney et al. sequenced the genome of the ornate burrowing frog (Platyplectrum ornatum), whose genome is smaller than that of many birds and exhibits bird-like characteristics, including reduced repetitive DNA content and reduced distances between genes. The sequences suggest several mechanisms that may be responsible for genome size reduction, including reduced abundance of transposable elements, increased deletion bias for transposable elements, reduction in the length of introns within genes, and expansion of the repertoire of genes that suppress transposable elements. Comparison with two other frog genera with small and large genomes suggests that reduction in genome size may occur in independent, convergent events and may be related to life history given that tadpole development and diet are similar among frog genera with reduced genome size. According to the authors, the study provides a framework for comparing genome reduction processes in other amphibians and vertebrates. — P.G.
PNAS e2011649118 (2021)
MICROBIOLOGY
Mutations in metabolic genes can cause antibiotic resistance
Researchers uncover a new category of mutations linked to antibiotic resistance. Image credit: Science Source/Doncaster and Bassetlaw Hospitals.
Posted on March 5, 2021
Amy McDermott
A recent study in Science reveals a novel avenue by which genetic changes make bacteria resistant to drugs: mutations in genes involved in cellular metabolism, including some that convert food into energy. “The genes were known; their involvement in metabolism was known; but it wasn’t known that mutations in these genes can cause resistance,” says lead author Allison Lopatkin, an assistant professor of computational biology at Barnard College of Columbia University in New York. Long term, the discovery could lead to new drug candidates. Continue Reading⇒