Functional synergy of a human-specific and an ape-specific metabolic regulator in human neocortex development.

Metabolism has recently emerged as a major target of genes implicated in the evolutionary expansion of human neocortex. One such gene is the human-specific gene ARHGAP11B. During human neocortex development, ARHGAP11B increases the abundance of basal radial glia, key progenitors for neocortex expansion, by stimulating glutaminolysis (glutamine-to-glutamate-to-alpha-ketoglutarate) in mitochondria. Here we show that the ape-specific protein GLUD2 (glutamate dehydrogenase 2), which also operates in mitochondria and converts glutamate-to-αKG, enhances ARHGAP11B's ability to increase basal radial glia abundance. ARHGAP11B + GLUD2 double-transgenic bRG show increased production of aspartate, a metabolite essential for cell proliferation, from glutamate via alpha-ketoglutarate and the TCA cycle. Hence, during human evolution, a human-specific gene exploited the existence of another gene that emerged during ape evolution, to increase, via concerted changes in metabolism, progenitor abundance and neocortex size.

The genetic changes that shaped Neandertals, Denisovans, and modern humans.

Modern human ancestors diverged from the ancestors of Neandertals and Denisovans about 600,000 years ago. Until about 40,000 years ago, these three groups existed in parallel, occasionally met, and exchanged genes. A critical question is why modern humans, and not the other two groups, survived, became numerous, and developed complex cultures. Here, we discuss genetic differences among the groups and some of their functional consequences. As more present-day genome sequences become available from diverse groups, we predict that very few, if any, differences will distinguish all modern humans from all Neandertals and Denisovans. We propose that the genetic basis of what constitutes a modern human is best thought of as a combination of genetic features, where perhaps none of them is present in each and every present-day individual.

Efficient high-precision homology-directed repair-dependent genome editing by HDRobust.

Homology-directed repair (HDR), a method for repair of DNA double-stranded breaks can be leveraged for the precise introduction of mutations supplied by synthetic DNA donors, but remains limited by low efficiency and off-target effects. In this study, we report HDRobust, a high-precision method that, via the combined transient inhibition of nonhomologous end joining and microhomology-mediated end joining, resulted in the induction of point mutations by HDR in up to 93% (median 60%, s.e.m. 3) of chromosomes in populations of cells. We found that, using this method, insertions, deletions and rearrangements at the target site, as well as unintended changes at other genomic sites, were largely abolished. We validated this approach for 58 different target sites and showed that it allows efficient correction of pathogenic mutations in cells derived from patients suffering from anemia, sickle cell disease and thrombophilia.

Major Genetic Risk Factors for Dupuytren's Disease Are Inherited From Neandertals.

Dupuytren's disease is characterized by fingers becoming permanently bent in a flexed position. Whereas people of African ancestry are rarely afflicted by Dupuytren's disease, up to ∼30% of men over 60 years suffer from this condition in northern Europe. Here, we meta-analyze 3 biobanks comprising 7,871 cases and 645,880 controls and find 61 genome-wide significant variants associated with Dupuytren's disease. We show that 3 of the 61 loci harbor alleles of Neandertal origin, including the second and third most strongly associated ones (P = 6.4 × 10-132 and P = 9.2 × 10-69, respectively). For the most strongly associated Neandertal variant, we identify EPDR1 as the causal gene. Dupuytren's disease is an example of how admixture with Neandertals has shaped regional differences in disease prevalence.

Ancient human DNA recovered from a Palaeolithic pendant.

Artefacts made from stones, bones and teeth are fundamental to our understanding of human subsistence strategies, behaviour and culture in the Pleistocene. Although these resources are plentiful, it is impossible to associate artefacts to specific human individuals1 who can be morphologically or genetically characterized, unless they are found within burials, which are rare in this time period. Thus, our ability to discern the societal roles of Pleistocene individuals based on their biological sex or genetic ancestry is limited2-5. Here we report the development of a non-destructive method for the gradual release of DNA trapped in ancient bone and tooth artefacts. Application of the method to an Upper Palaeolithic deer tooth pendant from Denisova Cave, Russia, resulted in the recovery of ancient human and deer mitochondrial genomes, which allowed us to estimate the age of the pendant at approximately 19,000-25,000 years. Nuclear DNA analysis identifies the presumed maker or wearer of the pendant as a female individual with strong genetic affinities to a group of Ancient North Eurasian individuals who lived around the same time but were previously found only further east in Siberia. Our work redefines how cultural and genetic records can be linked in prehistoric archaeology.

Response to Comment on "Human TKTL1 implies greater neurogenesis in frontal neocortex of modern humans than Neanderthals".

Herai et al. discuss the known fact that a low percentage of modern humans who lack any overt phenotypes carry the ancestral TKTL1 allele. Our paper demonstrates that the amino acid substitution in TKTL1 increases neural progenitor cells and neurogenesis in the developing brain. It is another question if, and to what extent, this has consequences for the adult brain.

Functional dissection of two amino acid substitutions unique to the human FOXP2 protein.

The transcription factor forkhead box P2 (FOXP2) is involved in the development of language and speech in humans. Two amino acid substitutions (T303N, N325S) occurred in the human FOXP2 after the divergence from the chimpanzee lineage. It has previously been shown that when they are introduced into the FOXP2 protein of mice they alter striatal synaptic plasticity by increasing long-term depression in medium spiny neurons. Here we introduce each of these amino acid substitutions individually into mice and analyze their effects in the striatum. We find that long-term depression in medium spiny neurons is increased in mice carrying only the T303N substitution to the same extent as in mice carrying both amino acid substitutions. In contrast, the N325S substitution has no discernable effects.

Detection of unintended on-target effects in CRISPR genome editing by DNA donors carrying diagnostic substitutions.

CRISPR nucleases can introduce double-stranded DNA breaks in genomes at positions specified by guide RNAs. When repaired by the cell, this may result in the introduction of insertions and deletions or nucleotide substitutions provided by exogenous DNA donors. However, cellular repair can also result in unintended on-target effects, primarily larger deletions and loss of heterozygosity due to gene conversion. Here we present a strategy that allows easy and reliable detection of unintended on-target effects as well as the generation of control cells that carry wild-type alleles but have demonstratively undergone genome editing at the target site. Our 'sequence-ascertained favorable editing' (SAFE) donor approach relies on the use of DNA donor mixtures containing the desired nucleotide substitutions or the wild-type alleles together with combinations of additional 'diagnostic' substitutions unlikely to have any effects. Sequencing of the target sites then results in that two different sequences are seen when both chromosomes are edited with 'SAFE' donors containing different sets of substitutions, while a single sequence indicates unintended effects such as deletions or gene conversion. We analyzed more than 850 human embryonic stem cell clones edited with 'SAFE' donors and detect all copy number changes and almost all clones with gene conversion.

The molecular evolution of spermatogenesis across mammals.

The testis produces gametes through spermatogenesis and evolves rapidly at both the morphological and molecular level in mammals1-6, probably owing to the evolutionary pressure on males to be reproductively successful7. However, the molecular evolution of individual spermatogenic cell types across mammals remains largely uncharacterized. Here we report evolutionary analyses of single-nucleus transcriptome data for testes from 11 species that cover the three main mammalian lineages (eutherians, marsupials and monotremes) and birds (the evolutionary outgroup), and include seven primates. We find that the rapid evolution of the testis was driven by accelerated fixation rates of gene expression changes, amino acid substitutions and new genes in late spermatogenic stages, probably facilitated by reduced pleiotropic constraints, haploid selection and transcriptionally permissive chromatin. We identify temporal expression changes of individual genes across species and conserved expression programs controlling ancestral spermatogenic processes. Genes predominantly expressed in spermatogonia (germ cells fuelling spermatogenesis) and Sertoli (somatic support) cells accumulated on X chromosomes during evolution, presumably owing to male-beneficial selective forces. Further work identified transcriptomal differences between X- and Y-bearing spermatids and uncovered that meiotic sex-chromosome inactivation (MSCI) also occurs in monotremes and hence is common to mammalian sex-chromosome systems. Thus, the mechanism of meiotic silencing of unsynapsed chromatin, which underlies MSCI, is an ancestral mammalian feature. Our study illuminates the molecular evolution of spermatogenesis and associated selective forces, and provides a resource for investigating the biology of the testis across mammals.

Genetic insights into the social organization of Neanderthals.

Genomic analyses of Neanderthals have previously provided insights into their population history and relationship to modern humans1-8, but the social organization of Neanderthal communities remains poorly understood. Here we present genetic data for 13 Neanderthals from two Middle Palaeolithic sites in the Altai Mountains of southern Siberia: 11 from Chagyrskaya Cave9,10 and 2 from Okladnikov Cave11-making this one of the largest genetic studies of a Neanderthal population to date. We used hybridization capture to obtain genome-wide nuclear data, as well as mitochondrial and Y-chromosome sequences. Some Chagyrskaya individuals were closely related, including a father-daughter pair and a pair of second-degree relatives, indicating that at least some of the individuals lived at the same time. Up to one-third of these individuals' genomes had long segments of homozygosity, suggesting that the Chagyrskaya Neanderthals were part of a small community. In addition, the Y-chromosome diversity is an order of magnitude lower than the mitochondrial diversity, a pattern that we found is best explained by female migration between communities. Thus, the genetic data presented here provide a detailed documentation of the social organization of an isolated Neanderthal community at the easternmost extent of their known range.

Human TKTL1 implies greater neurogenesis in frontal neocortex of modern humans than Neanderthals.

Neanderthal brains were similar in size to those of modern humans. We sought to investigate potential differences in neurogenesis during neocortex development. Modern human transketolase-like 1 (TKTL1) differs from Neanderthal TKTL1 by a lysine-to-arginine amino acid substitution. Using overexpression in developing mouse and ferret neocortex, knockout in fetal human neocortical tissue, and genome-edited cerebral organoids, we found that the modern human variant, hTKTL1, but not the Neanderthal variant, increases the abundance of basal radial glia (bRG) but not that of intermediate progenitors (bIPs). bRG generate more neocortical neurons than bIPs. The hTKTL1 effect requires the pentose phosphate pathway and fatty acid synthesis. Inhibition of these metabolic pathways reduces bRG abundance in fetal human neocortical tissue. Our data suggest that neocortical neurogenesis in modern humans differs from that in Neanderthals.

High-throughput muscle fiber typing from RNA sequencing data.

BACKGROUND: Skeletal muscle fiber type distribution has implications for human health, muscle function, and performance. This knowledge has been gathered using labor-intensive and costly methodology that limited these studies. Here, we present a method based on muscle tissue RNA sequencing data (totRNAseq) to estimate the distribution of skeletal muscle fiber types from frozen human samples, allowing for a larger number of individuals to be tested. METHODS: By using single-nuclei RNA sequencing (snRNAseq) data as a reference, cluster expression signatures were produced by averaging gene expression of cluster gene markers and then applying these to totRNAseq data and inferring muscle fiber nuclei type via linear matrix decomposition. This estimate was then compared with fiber type distribution measured by ATPase staining or myosin heavy chain protein isoform distribution of 62 muscle samples in two independent cohorts (n = 39 and 22). RESULTS: The correlation between the sequencing-based method and the other two were rATPas = 0.44 [0.13-0.67], [95% CI], and rmyosin = 0.83 [0.61-0.93], with p = 5.70 × 10-3 and 2.00 × 10-6, respectively. The deconvolution inference of fiber type composition was accurate even for very low totRNAseq sequencing depths, i.e., down to an average of ~ 10,000 paired-end reads. CONCLUSIONS: This new method ( https://github.com/OlaHanssonLab/PredictFiberType ) consequently allows for measurement of fiber type distribution of a larger number of samples using totRNAseq in a cost and labor-efficient way. It is now feasible to study the association between fiber type distribution and e.g. health outcomes in large well-powered studies.

The clinically relevant CYP2C8*3 and CYP2C9*2 haplotype is inherited from Neandertals.

Genetic variation in genes encoding cytochrome P450 enzymes influences the metabolism of drugs and endogenous compounds. The locus containing the cytochrome genes CYP2C8 and CYP2C9 on chromosome 10 exhibits linkage disequilibrium between the CYP2C8*3 and CYP2C9*2 alleles, forming a haplotype of ~300 kilobases. This haplotype is associated with altered metabolism of several drugs, most notably reduced metabolism of warfarin and phenytoin, leading to toxicity at otherwise therapeutic doses. Here we show that this haplotype is inherited from Neandertals.

Longer metaphase and fewer chromosome segregation errors in modern human than Neanderthal brain development.

Since the ancestors of modern humans separated from those of Neanderthals, around 100 amino acid substitutions spread to essentially all modern humans. The biological significance of these changes is largely unknown. Here, we examine all six such amino acid substitutions in three proteins known to have key roles in kinetochore function and chromosome segregation and to be highly expressed in the stem cells of the developing neocortex. When we introduce these modern human-specific substitutions in mice, three substitutions in two of these proteins, KIF18a and KNL1, cause metaphase prolongation and fewer chromosome segregation errors in apical progenitors of the developing neocortex. Conversely, the ancestral substitutions cause shorter metaphase length and more chromosome segregation errors in human brain organoids, similar to what we find in chimpanzee organoids. These results imply that the fidelity of chromosome segregation during neocortex development improved in modern humans after their divergence from Neanderthals.

The evolutionary history of human spindle genes includes back-and-forth gene flow with Neandertals.

Proteins associated with the spindle apparatus, a cytoskeletal structure that ensures the proper segregation of chromosomes during cell division, experienced an unusual number of amino acid substitutions in modern humans after the split from the ancestors of Neandertals and Denisovans. Here, we analyze the history of these substitutions and show that some of the genes in which they occur may have been targets of positive selection. We also find that the two changes in the kinetochore scaffold 1 (KNL1) protein, previously believed to be specific to modern humans, were present in some Neandertals. We show that the KNL1 gene of these Neandertals shared a common ancestor with present-day Africans about 200,000 years ago due to gene flow from the ancestors (or relatives) of modern humans into Neandertals. Subsequently, some non-Africans inherited this modern human-like gene variant from Neandertals, but none inherited the ancestral gene variants. These results add to the growing evidence of early contacts between modern humans and archaic groups in Eurasia and illustrate the intricate relationships among these groups.

A substitution in the glutathione reductase lowers electron leakage and inflammation in modern humans.

Glutathione reductase is a critical enzyme for preventing oxidative stress and maintaining a reduced intracellular environment. Almost all present-day humans carry an amino acid substitution (S232G) in this enzyme relative to apes and Neanderthals. We express the modern human and the ancestral enzymes and show that whereas the activity and stability are unaffected by the amino acid substitution, the ancestral enzyme produces more reactive oxygen species and increases cellular levels of transcripts encoding cytokines. We furthermore show that the ancestral enzyme has been reintroduced into the modern human gene pool by gene flow from Neanderthals and is associated with multiple traits in present-day people, including increased susceptibility for inflammatory-associated disorders and vascular disease.

Improved gRNA secondary structures allow editing of target sites resistant to CRISPR-Cas9 cleavage.

The first step in CRISPR-Cas9-mediated genome editing is the cleavage of target DNA sequences that are complementary to so-called spacer sequences in CRISPR guide RNAs (gRNAs). However, some DNA sequences are refractory to CRISPR-Cas9 cleavage, which is at least in part due to gRNA misfolding. To overcome this problem, we have engineered gRNAs with highly stable hairpins in their constant parts and further enhanced their stability by chemical modifications. The 'Genome-editing Optimized Locked Design' (GOLD)-gRNA increases genome editing efficiency up to around 1000-fold (from 0.08 to 80.5%) with a mean increase across different other targets of 7.4-fold. We anticipate that this improved gRNA will allow efficient editing regardless of spacer sequence composition and will be especially useful if a desired genomic site is difficult to edit.

Microstratigraphic preservation of ancient faunal and hominin DNA in Pleistocene cave sediments.

Ancient DNA recovered from Pleistocene sediments represents a rich resource for the study of past hominin and environmental diversity. However, little is known about how DNA is preserved in sediments and the extent to which it may be translocated between archaeological strata. Here, we investigate DNA preservation in 47 blocks of resin-impregnated archaeological sediment collected over the last four decades for micromorphological analyses at 13 prehistoric sites in Europe, Asia, Africa, and North America and show that such blocks can preserve DNA of hominins and other mammals. Extensive microsampling of sediment blocks from Denisova Cave in the Altai Mountains reveals that the taxonomic composition of mammalian DNA differs drastically at the millimeter-scale and that DNA is concentrated in small particles, especially in fragments of bone and feces (coprolites), suggesting that these are substantial sources of DNA in sediments. Three microsamples taken in close proximity in one of the blocks yielded Neanderthal DNA from at least two male individuals closely related to Denisova 5, a Neanderthal toe bone previously recovered from the same layer. Our work indicates that DNA can remain stably localized in sediments over time and provides a means of linking genetic information to the archaeological and ecological records on a microstratigraphic scale.

The earliest Denisovans and their cultural adaptation.

Since the initial identification of the Denisovans a decade ago, only a handful of their physical remains have been discovered. Here we analysed ~3,800 non-diagnostic bone fragments using collagen peptide mass fingerprinting to locate new hominin remains from Denisova Cave (Siberia, Russia). We identified five new hominin bones, four of which contained sufficient DNA for mitochondrial analysis. Three carry mitochondrial DNA of the Denisovan type and one was found to carry mtDNA of the Neanderthal type. The former come from the same archaeological layer near the base of the cave's sequence and are the oldest securely dated evidence of Denisovans at 200 ka (thousand years ago) (205-192 ka at 68.2% or 217-187 ka at 95% probability). The stratigraphic context in which they were located contains a wealth of archaeological material in the form of lithics and faunal remains, allowing us to determine the material culture associated with these early hominins and explore their behavioural and environmental adaptations. The combination of bone collagen fingerprinting and genetic analyses has so far more-than-doubled the number of hominin bones at Denisova Cave and has expanded our understanding of Denisovan and Neanderthal interactions, as well as their archaeological signatures.

Comment on "Reintroduction of the archaic variant of NOVA1 in cortical organoids alters neurodevelopment".

Trujillo et al. (Research Articles, 12 February 2021, eaax2537) conclude that the reintroduction of an ancestral amino acid substitution in the protein NOVA1 drastically alters the development of brain organoids. We show that cell lines used by the authors carry heterozygous deletions of the target DNA sequence, providing another plausible explanation for the effects observed.