Higher eukaryotic chromosomes are organized into topologically constrained functional domains; however, the molecular mechanisms required to sustain these complex interphase chromatin structures are unknown. A stable matrix underpinning nuclear organization was hypothesized, but the idea was abandoned as more dynamic models of chromatin behavior became prevalent. Here, we report that scaffold attachment factor A (SAF-A), originally identified as a structural nuclear protein, interacts with chromatin-associated RNAs (caRNAs) via its RGG domain to regulate human interphase chromatin structures in a transcription-dependent manner. Mechanistically, this is dependent on SAF-A’s AAA+ ATPase domain, which mediates cycles of protein oligomerization with caRNAs, in response to ATP binding and hydrolysis. SAF-A oligomerization decompacts large-scale chromatin structure while SAF-A loss or monomerization promotes aberrant chromosome folding and accumulation of genome damage. Our results show that SAF-A and caRNAs form a dynamic, transcriptionally responsive chromatin mesh that organizes large-scale chromosome structures and protects the genome from instability.

One hundred and seventy-three years ago, the last two Great Auks, Pinguinus impennis, ever reliably seen were killed. Their internal organs can be found in the collections of the Natural History Museum of Denmark, but the location of their skins has remained a mystery. In 1999, Great Auk expert Errol Fuller proposed a list of five potential candidate skins in museums around the world. Here we take a palaeogenomic approach to test which—if any—of Fuller’s candidate skins likely belong to either of the two birds. Using mitochondrial genomes from the five candidate birds (housed in museums in Bremen, Brussels, Kiel, Los Angeles, and Oldenburg) and the organs of the last two known individuals, we partially solve the mystery that has been on Great Auk scholars’ minds for generations and make new suggestions as to the whereabouts of the still-missing skin from these two birds.

Hybridization is a frequent and important force in plant evolution. Next-generation sequencing (NGS) methods offer new possibilities for clade resolution and ambitious sampling of gene genealogies, yet difficulty remains in detecting deep reticulation events using currently available methods. We reconstructed the phylogeny of diploid representatives of Amaryllidaceae tribe Hippeastreae to test the hypothesis of ancient hybridizations preceding the radiation of its major subclade, Hippeastrinae. Through hybrid enrichment of DNA libraries and NGS, we obtained data for 18 nuclear loci through a curated assembly approach and nearly complete plastid genomes for 35 ingroup taxa plus 5 outgroups. Additionally, we obtained alignments for 39 loci through an automated assembly algorithm. These data were analyzed with diverse phylogenetic methods, including concatenation, coalescence-based species tree estimation, Bayesian concordance analysis, and network reconstructions, to provide insights into the evolutionary relationships of Hippeastreae. Causes for gene tree heterogeneity and cytonuclear discordance were examined through a Bayesian posterior predictive approach (JML) and coalescent simulations. Two major clades were found, Hippeastrinae and Traubiinae, as previously reported. Our results suggest the presence of two major nuclear lineages in Hippeastrinae characterized by different chromosome numbers: (1) Tocantinia and Hippeastrum with 2n = 22, and (2) Eithea, Habranthus, Rhodophiala, and Zephyranthes mostly with 2n = 12, 14, and 18. Strong cytonuclear discordance was confirmed in Hippeastrinae, and a network scenario with at least six hybridization events is proposed to reconcile nuclear and plastid signals, along a backbone that may also have been affected by incomplete lineage sorting at the base of each major subclade.

* Targeted enrichment of conserved genomic regions (e.g. ultraconserved elements or UCEs) has emerged as a promising tool for inferring evolutionary history in many organismal groups. Because the UCE approach is still relatively new, much remains to be learned about how best to identify UCE loci and design baits to enrich them. * We test an updated UCE identification and bait design workflow for the insect order Hymenoptera, with a particular focus on ants. The new strategy augments a previous bait design for Hymenoptera by (i) changing the parameters by which conserved genomic regions are identified and retained, and (ii) increasing the number of genomes used for locus identification and bait design. We perform in vitro validation of the approach in ants by synthesizing an ant-specific bait set that targets UCE loci and a set of ‘legacy’ phylogenetic markers. Using this bait set, we generate new data for 84 taxa (16/17 ant subfamilies) and extract loci from an additional 17 genome-enabled taxa. We then use these data to examine UCE capture success and phylogenetic performance across ants. We also test the workability of extracting legacy markers from enriched samples and combining the data with published datasets. * The updated bait design (hym-v2) contained a total of 2590-targeted UCE loci for Hymenoptera, significantly increasing the number of loci relative to the original bait set (hym-v1; 1510 loci). Across 38 genome-enabled Hymenoptera and 84 enriched samples, experiments demonstrated a high and unbiased capture success rate, with the mean locus enrichment rate being 2214 loci per sample. Phylogenomic analyses of ants produced a robust tree that included strong support for previously uncertain relationships. Complementing the UCE results, we successfully enriched legacy markers, combined the data with published Sanger datasets and generated a comprehensive ant phylogeny containing 1060 terminals. * Overall, the new UCE bait design strategy resulted in an enhanced bait set for genome-scale phylogenetics in ants and other Hymenoptera. Our in vitro tests demonstrate the utility of the updated design workflow, providing evidence that this approach could be applied to any organismal group with available genomic information.

The sinipercids are freshwater fishes endemic to East Asia, mainly in China. Phylogenetic studies on the sinipercids have made great progress in the last decades, but interspecific relationships and evolutionary history of the sinipercids remain unresolved. Lack of distinctive morphological characters leads to problems in validating of some species, such as Siniperca loona. Moreover, genetic data are needed to delimitate species pairs with explicit hypothesis testing, such as in S. chuatsi vs. S. kneri and Coreoperca whiteheadi vs. C. liui. Here we reconstructed phylogeny of the sinipercids with an unprecedented scale of data, 16,943 loci of single-copy coding sequence data from nine sinipercid species, eight putative sister taxa and two outgroups. Targeted sequences were collected using gene enrichment and Illumina sequencing, yielding thousands of protein coding sequences and single nucleotide polymorphisms (SNPs) data. Maximum likelihood and coalescent species tree analyses resulted in identical and highly supported trees. We confirmed that the centrarchids are sister to the sinipercids. A monophyletic Sinipercidae with two genera, Siniperca and Coreoperca was also supported. Different from most previous studies, S. scherzeri was found as the most basal taxon to other species of Siniperca, which consists of two clades: a clade having S. roulei sister to S. chuatsi and S. kneri, and a clade consisting S. loona sister to S. obscura and S. undulata. We found that both S. loona and C. liui are valid species using Bayes factor delimitation (BFD∗) based on SNPs data. Species delimitation also provided decisive support for S. chuatsi and S. kneri being two distinct species. We calibrated a chronogram of the sinipercids based on 100 loci and three fossil calibration points using BEAST, and reconstructed ancestral ranges of the sinipercids using Lagrange Analysis (DEC model) and Statistical Dispersal-Vicariance Analysis (S-DIVA) implemented in RASP. Divergence time estimates and ancestral habitat reconstruction suggested a wide-ranging distribution of the common ancestor of the sinipercids in southern China at 53.1 million years ago (CI: 30.4–85.8Ma). The calibrated time tree is consistent with historical climate changes and geological events that might have shaped the current distribution of the sinipercids.

While hybridization has recently received a resurgence of attention from systematists and evolutionary biologists, there remains a dearth of case studies on ancient, diversified hybrid lineages—clades of organisms that originated through reticulation. Studies on these groups are valuable in that they would speak to the long-term phylogenetic success of lineages following gene flow between species. We present a phylogenomic view of Heuchera, long known for frequent hybridization, incorporating all three independent genomes: targeted nuclear (~400,000 bp), plastid (~160,000 bp), and mitochondrial (~470,000 bp) data. We analyze these data using multiple concatenation and coalescence strategies. The nuclear phylogeny is consistent with previous work and with morphology, confidently suggesting a monophyletic Heuchera. By contrast, analyses of both organellar genomes recover a grossly polyphyletic Heuchera,consisting of three primary clades with relationships extensively rearranged within these as well. A minority of nuclear loci also exhibit phylogenetic discord; yet these topologies remarkably never resemble the pattern of organellar loci and largely present low levels of discord inter alia. Two independent estimates of the coalescent branch length of the ancestor of Heuchera using nuclear data suggest rare or nonexistent incomplete lineage sorting with related clades, inconsistent with the observed gross polyphyly of organellar genomes (confirmed by simulation of gene trees under the coalescent). These observations, in combination with previous work, strongly suggest hybridization as the cause of this phylogenetic discord.

High-throughput sequencing has dramatically fostered ancient DNA research in recent years. Shotgun sequencing, however, does not necessarily appear as the best-suited approach due to the extensive contamination of samples with exogenous environmental microbial DNA. DNA capture-enrichment methods represent cost-effective alternatives that increase the sequencing focus on the endogenous fraction, whether it is from mitochondrial or nuclear genomes, or parts thereof. Here, we explored experimental parameters that could impact the efficacy of MYbaits in-solution capture assays of ~5000 nuclear loci or the whole genome. We found that varying quantities of the starting probes had only moderate effect on capture outcomes. Starting DNA, probe tiling, the hybridization temperature and the proportion of endogenous DNA all affected the assay, however. Additionally, probe features such as their GC content, number of CpG dinucleotides, sequence complexity and entropy and self-annealing properties need to be carefully addressed during the design stage of the capture assay. The experimental conditions and probe molecular features identified in this study will improve the recovery of genetic information extracted from degraded and ancient remains.