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Complex multicellularity has emerged independently across a few eukaryotic lineages and is often associated with the rise of elaborate, tightly coordinated developmental processes1,2. How multicellularity and development are interconnected in evolution is a major question in biology. The hourglass model of embryonic evolution depicts how developmental processes are conserved during evolution, and predicts morphological and molecular divergence in early and late embryogenesis, bridged by a conserved mid-embryonic (phylotypic) period linked to the formation of the basic body plan3,4. Initially found in animal embryos5–8, molecular hourglass patterns have recently been proposed for land plants and fungi9,10. However, whether the hourglass pattern is an intrinsic feature of all complex multicellular eukaryotes remains unknown. Here we tested the presence of a molecular hourglass in the brown algae, a eukaryotic lineage that has evolved multicellularity independently from animals, fungi and plants1,11,12. By exploring transcriptome evolution patterns of brown algae with distinct morphological complexities, we uncovered an hourglass pattern during embryogenesis in morphologically complex species. Filamentous algae without canonical embryogenesis display transcriptome conservation in multicellular stages of the life cycle, whereas unicellular stages are more rapidly evolving. Our findings suggest that transcriptome conservation in brown algae is associated with cell differentiation stages, but is not necessarily linked to embryogenesis. Together with previous work in animals, plants and fungi, we provide further evidence for the generality of a developmental hourglass pattern across complex multicellular eukaryotes.

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1–6in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.

The loss of the tail is among the most notable anatomical changes to have occurred along the evolutionary lineage leading to humans and to the ‘anthropomorphous apes’1–3, with a proposed role in contributing to human bipedalism4–6. Yet, the genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown. Here we present evidence that an individual insertion of an Alu element in the genome of the hominoid ancestor may have contributed to tail-loss evolution. We demonstrate that this Alu element—inserted into an intron of the TBXTgene7–9—pairs with a neighbouring ancestral Alu element encoded in the reverse genomic orientation and leads to a hominoid-specific alternative splicing event. To study the effect of this splicing event, we generated multiple mouse models that express both full-length and exon-skipped isoforms of Tbxt, mimicking the expression pattern of its hominoid orthologue TBXT. Mice expressing both Tbxtisoforms exhibit a complete absence of the tail or a shortened tail depending on the relative abundance of Tbxtisoforms expressed at the embryonic tail bud. These results support the notion that the exon-skipped transcript is sufficient to induce a tail-loss phenotype. Moreover, mice expressing the exon-skipped Tbxtisoform develop neural tube defects, a condition that affects approximately 1 in 1,000 neonates in humans10. Thus, tail-loss evolution may have been associated with an adaptive cost of the potential for neural tube defects, which continue to affect human health today.

Many of the Earth’s microbes remain uncultured and understudied, limiting our understanding of the functional and evolutionary aspects of their genetic material, which remain largely overlooked in most metagenomic studies1. Here we analysed 149,842 environmental genomes from multiple habitats2–6and compiled a curated catalogue of 404,085 functionally and evolutionarily significant novel (FESNov) gene families exclusive to uncultivated prokaryotic taxa. All FESNov families span multiple species, exhibit strong signals of purifying selection and qualify as new orthologous groups, thus nearly tripling the number of bacterial and archaeal gene families described to date. The FESNov catalogue is enriched in clade-specific traits, including 1,034 novel families that can distinguish entire uncultivated phyla, classes and orders, probably representing synapomorphies that facilitated their evolutionary divergence. Using genomic context analysis and structural alignments we predicted functional associations for 32.4% of FESNov families, including 4,349 high-confidence associations with important biological processes. These predictions provide a valuable hypothesis-driven framework that we used for experimental validatation of a new gene family involved in cell motility and a novel set of antimicrobial peptides. We also demonstrate that the relative abundance profiles of novel families can discriminate between environments and clinical conditions, leading to the discovery of potentially new biomarkers associated with colorectal cancer. We expect this work to enhance future metagenomics studies and expand our knowledge of the genetic repertory of uncultivated organisms.

Genomic instability arising from defective responses to DNA damage1or mitotic chromosomal imbalances2can lead to the sequestration of DNA in aberrant extranuclear structures called micronuclei (MN). Although MN are a hallmark of ageing and diseases associated with genomic instability, the catalogue of genetic players that regulate the generation of MN remains to be determined. Here we analyse 997 mouse mutant lines, revealing 145 genes whose loss significantly increases (n= 71) or decreases (n= 74) MN formation, including many genes whose orthologues are linked to human disease. We found that mice null for Dscc1, which showed the most significant increase in MN, also displayed a range of phenotypes characteristic of patients with cohesinopathy disorders. After validating the DSCC1-associated MN instability phenotype in human cells, we used genome-wide CRISPR–Cas9 screening to define synthetic lethal and synthetic rescue interactors. We found that the loss of SIRT1can rescue phenotypes associated with DSCC1loss in a manner paralleling restoration of protein acetylation of SMC3. Our study reveals factors involved in maintaining genomic stability and shows how this information can be used to identify mechanisms that are relevant to human disease biology1.

Tropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, Ψ50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3–5, little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters Ψ50and HSM50vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both Ψ50and HSM50influence the biogeographical distribution of Amazon tree species. However, HSM50was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50are gaining more biomass than are low HSM50forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50in the Amazon6,7, with strong implications for the Amazon carbon sink.

Climate’s effect on global biodiversity is typically viewed through the lens of temperature, humidity and resulting ecosystem productivity1–6. However, it is not known whether biodiversity depends solely on these climate conditions, or whether the size and fragmentation of these climates are also crucial. Here we shift the common perspective in global biodiversity studies, transitioning from geographic space to a climate-defined multidimensional space. Our findings suggest that larger and more isolated climate conditions tend to harbour higher diversity and species turnover among terrestrial tetrapods, encompassing more than 30,000 species. By considering both the characteristics of climate itself and its geographic attributes, we can explain almost 90% of the variation in global species richness. Half of the explanatory power (45%) may be attributed either to climate itself or to the geography of climate, suggesting a nuanced interplay between them. Our work evolves the conventional idea that larger climate regions, such as the tropics, host more species primarily because of their size7,8. Instead, we underscore the integral roles of both the geographic extent and degree of isolation of climates. This refined understanding presents a more intricate picture of biodiversity distribution, which can guide our approach to biodiversity conservation in an ever-changing world.

The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.

During the transition from a healthy state to cardiometabolic disease, patients become heavily medicated, which leads to an increasingly aberrant gut microbiome and serum metabolome, and complicates biomarker discovery1–5. Here, through integrated multi-omics analyses of 2,173 European residents from the MetaCardis cohort, we show that the explanatory power of drugs for the variability in both host and gut microbiome features exceeds that of disease. We quantify inferred effects of single medications, their combinations as well as additive effects, and show that the latter shift the metabolome and microbiome towards a healthier state, exemplified in synergistic reduction in serum atherogenic lipoproteins by statins combined with aspirin, or enrichment of intestinal Roseburiaby diuretic agents combined with beta-blockers. Several antibiotics exhibit a quantitative relationship between the number of courses prescribed and progression towards a microbiome state that is associated with the severity of cardiometabolic disease. We also report a relationship between cardiometabolic drug dosage, improvement in clinical markers and microbiome composition, supporting direct drug effects. Taken together, our computational framework and resulting resources enable the disentanglement of the effects of drugs and disease on host and microbiome features in multimedicated individuals. Furthermore, the robust signatures identified using our framework provide new hypotheses for drug–host–microbiome interactions in cardiometabolic disease.

Microbial genes encode the majority of the functional repertoire of life on earth. However, despite increasing efforts in metagenomic sequencing of various habitats1–3, little is known about the distribution of genes across the global biosphere, with implications for human and planetary health. Here we constructed a non-redundant gene catalogue of 303 million species-level genes (clustered at 95% nucleotide identity) from 13,174 publicly available metagenomes across 14 major habitats and use it to show that most genes are specific to a single habitat. The small fraction of genes found in multiple habitats is enriched in antibiotic-resistance genes and markers for mobile genetic elements. By further clustering these species-level genes into 32 million protein families, we observed that a small fraction of these families contain the majority of the genes (0.6% of families account for 50% of the genes). The majority of species-level genes and protein families are rare. Furthermore, species-level genes, and in particular the rare ones, show low rates of positive (adaptive) selection, supporting a model in which most genetic variability observed within each protein family is neutral or nearly neutral.

Microbiome community typing analyses have recently identified the Bacteroides2 (Bact2) enterotype, an intestinal microbiota configuration that is associated with systemic inflammation and has a high prevalence in loose stools in humans1,2. Bact2 is characterized by a high proportion of Bacteroides, a low proportion of Faecalibacteriumand low microbial cell densities1,2, and its prevalence varies from 13% in a general population cohort to as high as 78% in patients with inflammatory bowel disease2. Reported changes in stool consistency3and inflammation status4during the progression towards obesity and metabolic comorbidities led us to propose that these developments might similarly correlate with an increased prevalence of the potentially dysbiotic Bact2 enterotype. Here, by exploring obesity-associated microbiota alterations in the quantitative faecal metagenomes of the cross-sectional MetaCardis Body Mass Index Spectrum cohort (n= 888), we identify statin therapy as a key covariate of microbiome diversification. By focusing on a subcohort of participants that are not medicated with statins, we find that the prevalence of Bact2 correlates with body mass index, increasing from 3.90% in lean or overweight participants to 17.73% in obese participants. Systemic inflammation levels in Bact2-enterotyped individuals are higher than predicted on the basis of their obesity status, indicative of Bact2 as a dysbiotic microbiome constellation. We also observe that obesity-associated microbiota dysbiosis is negatively associated with statin treatment, resulting in a lower Bact2 prevalence of 5.88% in statin-medicated obese participants. This finding is validated in both the accompanying MetaCardis cardiovascular disease dataset (n= 282) and the independent Flemish Gut Flora Project population cohort (n =2,345). The potential benefits of statins in this context will require further evaluation in a prospective clinical trial to ascertain whether the effect is reproducible in a randomized population and before considering their application as microbiota-modulating therapeutics.

Ultrahot giant exoplanets receive thousands of times Earth’s insolation1,2. Their high-temperature atmospheres (greater than 2,000 kelvin) are ideal laboratories for studying extreme planetary climates and chemistry3–5. Daysides are predicted to be cloud-free, dominated by atomic species6and much hotter than nightsides5,7,8. Atoms are expected to recombine into molecules over the nightside9, resulting in different day and night chemistries. Although metallic elements and a large temperature contrast have been observed10–14, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night (‘evening’) and night-to-day (‘morning’) terminators could, however, be revealed as an asymmetric absorption signature during transit4,7,15. Here we report the detection of an asymmetric atmospheric signature in the ultrahot exoplanet WASP-76b. We spectrally and temporally resolve this signature using a combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by −11 ± 0.7 kilometres per second on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside16. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. We conclude that iron must therefore condense during its journey across the nightside.

Genetic instability, a heritable increase in the rate of genetic mutation, accelerates evolutionary adaptation1and is widespread in cancer2,3. In mammals, instability can arise from damage to both copies of genes involved in DNA metabolism and cell cycle regulation4or from inactivation of one copy of a gene whose product is present in limiting amounts (haploinsufficiency5); however, it has proved difficult to determine the relative importance of these two mechanisms. In Escherichia coli6, the application of repeated, strong selection enriches for genetic instability. Here we have used this approach to evolve genetic instability in diploid cells of the budding yeast Saccharomyces cerevisiae, and have isolated clones with increased rates of point mutation, mitotic recombination, and chromosome loss. We identified candidate, heterozygous, instability-causing mutations; engineering these mutations, as heterozygotes, into the ancestral diploid strain caused genetic instability. Mutations that inactivated one copy of haploinsufficient genes were more common than those that dominantly altered the function of the mutated gene copy. The mutated genes were enriched for genes functioning in transport, protein quality control, and DNA metabolism, and have revealed new targets for genetic instability7–11, including essential genes. Although only a minority (10 out of 57 genes with orthologues or close homologues) of the targets we identified have homologous human genes that have been implicated in cancer2, the remainder are candidates to contribute to human genetic instability. To test this hypothesis, we inactivated six examples in a near-haploid human cell line; five of these mutations increased instability. We conclude that single genetic events cause genetic instability in diploid yeast cells, and propose that similar, heterozygous mutations in mammalian homologues initiate genetic instability in cancer.

Soils harbour some of the most diverse microbiomes on Earth and are essential for both nutrient cycling and carbon storage. To understand soil functioning, it is necessary to model the global distribution patterns and functional gene repertoires of soil microorganisms, as well as the biotic and environmental associations between the diversity and structure of both bacterial and fungal soil communities1–4. Here we show, by leveraging metagenomics and metabarcoding of global topsoil samples (189 sites, 7,560 subsamples), that bacterial, but not fungal, genetic diversity is highest in temperate habitats and that microbial gene composition varies more strongly with environmental variables than with geographic distance. We demonstrate that fungi and bacteria show global niche differentiation that is associated with contrasting diversity responses to precipitation and soil pH. Furthermore, we provide evidence for strong bacterial–fungal antagonism, inferred from antibiotic-resistance genes, in topsoil and ocean habitats, indicating the substantial role of biotic interactions in shaping microbial communities. Our results suggest that both competition and environmental filtering affect the abundance, composition and encoded gene functions of bacterial and fungal communities, indicating that the relative contributions of these microorganisms to global nutrient cycling varies spatially. Metagenomic, chemical and biomass analyses of topsoil samples from around the world reveal spatial and environmental trends in microbial community composition and genetic diversity.

Virus genomes reveal the establishment of Zika virus in Brazil and the Americas, and provide an appropriate timeframe for baseline (pre-Zika) microcephaly in different regions.

CORTISONE1and hydrocortisone2can prolong the lifespan of human embryonic fibroblasts cultivated in vitro and this prolongation is accompanied by a significant increase in the saturation density. The same effect has been observed in cultures of primary human amnion cells3. One of the constant features during senescence in vitro of cells from different species is the progressive decrease of the cell density at which growth practically stops, and it has been suggested4that the two phenomena, ageing in vitro and decrease of the saturation density, are related.

IT is well known that chicken fibroblasts invariably die after a certain number of doublings in vitro(cell senescence) and that they have never been established by any chemical or physical agent1. On the other hand, mouse fibroblasts invariably acquire spontaneously an infinite growth potential, and transformation can be induced at a high frequency by different oncogenes2. Other species like man also yield fibroblasts which never acquire spontaneously the capacity to divide for ever3but can become permanent cell lines after infection with SV40 virus4. Transformation in human fibroblasts has only been unequivocally demonstrated after treatment with certain viruses. This behaviour of fibroblasts in vitrohas been attributed to different nutritional requirements5. The two approaches to explain the phenomenon can be summarised as intrinsic properties against environmental conditions. We have previously shortened the life-spans of cultivated chicken fibroblasts with low dose rate ionising radiation6. We have carried out the same type of experiment with human and mouse fibroblasts and found that the response to ionising radiation fits the relative tendencies of these different fibroblasts to yield permanent cell lines.

THE idea that an increased number of non-dividing cells accumulate during the growth decline of human embryonic fibroblasts (HEF) cultivated in vitro has been put forward1. This concept of a non-dividing fraction of cells seems to be widely accepted2,3, but no compelling evidence exists so far, to show that non-cycling cells exist in old cultures of human fibroblasts. On the contrary, it seems that most, if not all, the cells can divide up to the end of the lifespan of human diploid cell lines. What seems to take place, however, is an increased transit time and heterogeneity of cell cycles4,5.

USING the single-burst technique we have been able to show that close to one-half of the cells in a lysogenic culture of phage Mu yield no viable phage after induction. Our experiments were prompted by an intriguing observation concerning the G segment of Mu, a region of 3,000 base pairs found in either orientation in both mature phages and prophages1,2; it is thought that G inversions are mediated by inverted repeats of approximately 50 base pairs known to be located at the two ends of G (ref. 3). It was observed that progeny phage derived from the induction of lysogenic cultures contain approximately equal numbers of particles with the G segment in either orientation, but virtually all progeny phage derived from lytic cycles of infection have their G segment in one particular orientation4.

ROUS sarcoma virus (RSV) suspensions can induce the synthesis of deoxyribonucleic acid (DNA) and mitosis in resting stage human fibroblasts1. The virus can also induce DNA synthesis in undividing myotubes2and DNA synthesis and mitosis in resting stage chick embryo fibroblasts3,4. The stimulatory activity may not be identifiable with the virus particle, for when the virus suspension was treated with RSV anti-serum the focus forming capacity was inhibited but the stimulatory action was not eliminated1. We have now extended these findings. The WI-38 human embryonic line5was used maintained in Eagle's minimal essential medium6supplemented with 10 per cent calf serum and aureomycin (50 µg/ml.). RSV suspensions were obtained from the supernatants of infected chick embryo fibroblastic cultures, and had a titre of 105FFU/ml. DNA synthesis was estimated by adding 0.1 µCi/ml. of labelled thymidine (3H-TdR) (specific activity, 14 Ci/mmole) to the cultures. The cells were fixed 24 h later, DNA was extracted7and the radioactivity incorporated was measured in a liquid scintillation counter.

THE Liebermann-Burchard reaction1is extensively used for the characterization of polynuclear compounds (steroids, polyterpenoids, etc.). Applying this reaction to some of these compounds and simpler ones, according to the conditions described by Nath, Chakravorty and Chowdhury2, with enough chloroform to give a homogeneous medium, colloidal solutions are obtained. With cholesterol, β-amyrenol, abietic acid, limonene, cyclohexanone and linalool, the solutions are strongly coloured and show a strong Tyndall effect and Brownian movement by the ultramicroscope.

WE have used divergent field (wire-cylinder and point-plane) electrode configurations to study the emission under high field of electrons from a metal into a liquid dielectric—in particular, liquid nitrogen. After outgassing the emitting electrode under high vacuum, high purity gas is condensed under slight overpressure, while taking proper steps to avoid the presence of dust or impurities.