Reconstruction of hundreds of reference ancestral genomes across the eukaryotic kingdom

Genome organization: Raison d'être of ancestral linkage groups

The genomes of extant organisms contain conserved blocks of regions that can be traced back to ancient ancestors, yet the evolutionary pressures that maintained such genomic segments remain unclear. New research on a curious organism with two different genomes sheds light on why our genomes are organized as they are.

Chromosome-level genome assemblies of 2 hemichordates provide new insights into deuterostome origin and chromosome evolution

Deuterostomes are a monophyletic group of animals that includes Hemichordata, Echinodermata (together called Ambulacraria), and Chordata. The diversity of deuterostome body plans has made it challenging to reconstruct their ancestral condition and to decipher the genetic changes that drove the diversification of deuterostome lineages. Here, we generate chromosome-level genome assemblies of 2 hemichordate species, Ptychodera flava and Schizocardium californicum, and use comparative genomic approaches to infer the chromosomal architecture of the deuterostome common ancestor and delineate lineage-specific chromosomal modifications. We show that hemichordate chromosomes (1N = 23) exhibit remarkable chromosome-scale macrosynteny when compared to other deuterostomes and can be derived from 24 deuterostome ancestral linkage groups (ALGs). These deuterostome ALGs in turn match previously inferred bilaterian ALGs, consistent with a relatively short transition from the last common bilaterian ancestor to the origin of deuterostomes. Based on this deuterostome ALG complement, we deduced chromosomal rearrangement events that occurred in different lineages. For example, a fusion-with-mixing event produced an Ambulacraria-specific ALG that subsequently split into 2 chromosomes in extant hemichordates, while this homologous ALG further fused with another chromosome in sea urchins. Orthologous genes distributed in these rearranged chromosomes are enriched for functions in various developmental processes. We found that the deeply conserved Hox clusters are located in highly rearranged chromosomes and that maintenance of the clusters are likely due to lower densities of transposable elements within the clusters. We also provide evidence that the deuterostome-specific pharyngeal gene cluster was established via the combination of 3 pre-assembled microsyntenic blocks. We suggest that since chromosomal rearrangement events and formation of new gene clusters may change the regulatory controls of developmental genes, these events may have contributed to the evolution of diverse body plans among deuterostomes.

Evolutionary divergence of TLR9 through ancestral sequence reconstruction

The transmembrane pattern recognition receptor, Toll-like receptor (TLR), are best known for their roles in innate immunity via recognition of pathogen and initiation of signaling response. Mammalian TLRs recognize molecular patterns associated with pathogens and initiate innate immune response. We have studied the evolutionary diversity of mammalian TLR genes for differences in immunological response. Reconstruction of ancestral sequences is a key aspect of the molecular evolution of TLR to track changes across the TLR genes. The comprehensive analysis of mammalian TLRs revealed a distinct pattern of evolution of TLR9. Various sequence-based features such as amino acid usage, hydrophobicity, GC content, and evolutionary constraints are found to influence the divergence of TLR9 from other TLRs. Ancestral sequence reconstruction analysis also revealed that the gradual evolution of TLR genes in several ancestral lineages leads to the distinct pattern of TLR9. It demonstrates evolutionary divergence with the progressive accumulation of mutations results in the distinct pattern of TLR9.

Pan-evolutionary and regulatory genome architecture delineated by an integrated macro- and microsynteny approach

The forthcoming massive genome data generated by the Earth BioGenome Project will open up a new era of comparative genomics, for which genome synteny analysis provides an important framework. Profiling genome synteny represents an essential step in elucidating genome architecture, regulatory blocks/elements and their evolutionary history. Here we describe PanSyn, ( https://github.com/yhw320/PanSyn ), the most comprehensive and up-to-date genome synteny pipeline, providing step-by-step instructions and application examples to demonstrate its usage. PanSyn inherits both basic and advanced functions from existing popular tools, offering a user-friendly, highly customized approach for genome macrosynteny analysis and integrated pan-evolutionary and regulatory analysis of genome architecture, which are not yet available in public synteny software or tools. The advantages of PanSyn include: (i) advanced microsynteny analysis by functional profiling of microsynteny genes and associated regulatory elements; (ii) comprehensive macrosynteny analysis, including the inference of karyotype evolution from ancestors to extant species; and (iii) functional integration of microsynteny and macrosynteny for pan-evolutionary profiling of genome architecture and regulatory blocks, as well as integration with external functional genomics datasets from three- or four-dimensional genome and ENCODE projects. PanSyn requires basic knowledge of the Linux environment and Perl programming language and the ability to access a computer cluster, especially for large-scale genomic comparisons. Our protocol can be easily implemented by a competent graduate student or postdoc and takes several days to weeks to execute for dozens to hundreds of genomes. PanSyn provides yet the most comprehensive and powerful tool for integrated evolutionary and functional genomics.

Complete telomere-to-telomere genomes uncover virulence evolution conferred by chromosome fusion in oomycete plant pathogens

Variations in chromosome number are occasionally observed among oomycetes, a group that includes many plant pathogens, but the emergence of such variations and their effects on genome and virulence evolution remain ambiguous. We generated complete telomere-to-telomere genome assemblies for Phytophthora sojae, Globisporangium ultimum, Pythium oligandrum, and G. spinosum. Reconstructing the karyotype of the most recent common ancestor in Peronosporales revealed that frequent chromosome fusion and fission drove changes in chromosome number. Centromeres enriched with Copia-like transposons may contribute to chromosome fusion and fission events. Chromosome fusion facilitated the emergence of pathogenicity genes and their adaptive evolution. Effectors tended to duplicate in the sub-telomere regions of fused chromosomes, which exhibited evolutionary features distinct to the non-fused chromosomes. By integrating ancestral genomic dynamics and structural predictions, we have identified secreted Ankyrin repeat-containing proteins (ANKs) as a novel class of effectors in P. sojae. Phylogenetic analysis and experiments further revealed that ANK is a specifically expanded effector family in oomycetes. These results revealed chromosome dynamics in oomycete plant pathogens, and provided novel insights into karyotype and effector evolution.

SYNY: a pipeline to investigate and visualize collinearity between genomes

Investigating collinearity between chromosomes is often used in comparative genomics to help identify gene orthologs, pinpoint genes that might have been overlooked as part of annotation processes and/or perform various evolutionary inferences. Collinear segments, also known as syntenic blocks, can be inferred from sequence alignments and/or from the identification of genes arrayed in the same order and relative orientations between investigated genomes. To help perform these analyses and assess their outcomes, we built a simple pipeline called SYNY (for synteny) that implements the two distinct approaches and produces different visualizations. The SYNY pipeline was built with ease of use in mind and runs on modest hardware. The pipeline is written in Perl and Python and is available on GitHub (https://github.com/PombertLab/SYNY) under the permissive MIT license.

Mitochondrial genome fragmentation is correlated with increased rates of molecular evolution

While mitochondrial genome content and organization is quite diverse across all Eukaryotes, most bilaterian animal mitochondrial genomes (mitogenomes) exhibit highly conserved gene content and organisation, with genes typically encoded on a single circular chromosome. However, many species of parasitic lice (Insecta: Phthiraptera) are among the notable exceptions, having mitogenomes fragmented into multiple circular chromosomes. To better understand the process of mitogenome fragmentation, we conducted a large-scale genomic study of a major group of lice, Amblycera, with extensive taxon sampling. Analyses of the evolution of mitogenome structure across a phylogenomic tree of 90 samples from 53 genera revealed evidence for multiple independent origins of mitogenome fragmentation, some inferred to have occurred less than five million years ago. We leveraged these many independent origins of fragmentation to compare the rates of DNA substitution and gene rearrangement, specifically contrasting branches with fragmented and non-fragmented mitogenomes. We found that lineages with fragmented mitochondrial genomes had significantly higher rates of mitochondrial sequence evolution. In addition, lineages with fragmented mitochondrial genomes were more likely to have mitogenome gene rearrangements than those with single-chromosome mitochondrial genomes. By combining phylogenomics and mitochondrial genomics we provide a detailed portrait of mitogenome evolution across this group of insects with a remarkably unstable mitogenome structure, identifying processes of molecular evolution that are correlated with mitogenome fragmentation.

Comparative genomics reveals the dynamics of chromosome evolution in Lepidoptera

Chromosomes are a central unit of genome organization. One-tenth of all described species on Earth are butterflies and moths, the Lepidoptera, which generally possess 31 chromosomes. However, some species display dramatic variation in chromosome number. Here we analyse 210 chromosomally complete lepidopteran genomes and show that the chromosomes of extant lepidopterans are derived from 32 ancestral linkage groups, which we term Merian elements. Merian elements have remained largely intact through 250 million years of evolution and diversification. Against this stable background, eight lineages have undergone extensive reorganization either through numerous fissions or a combination of fusion and fission events. Outside these lineages, fusions are rare and fissions are rarer still. Fusions often involve small, repeat-rich Merian elements and the sex-linked element. Our results reveal the constraints on genome architecture in Lepidoptera and provide a deeper understanding of chromosomal rearrangements in eukaryotic genome evolution.

The Genome of Plasmodium gonderi: Insights into the Evolution of Human Malaria Parasites

Plasmodium species causing malaria in humans are not monophyletic, sharing common ancestors with nonhuman primate parasites. Plasmodium gonderi is one of the few known Plasmodium species infecting African old-world monkeys that are not found in apes. This study reports a de novo assembled P. gonderi genome with complete chromosomes. The P. gonderi genome shares codon usage, syntenic blocks, and other characteristics with the human parasites Plasmodium ovale s.l. and Plasmodium malariae, also of African origin, and the human parasite Plasmodium vivax and species found in nonhuman primates from Southeast Asia. Using phylogenetically aware methods, newly identified syntenic blocks were found enriched with conserved metabolic genes. Regions outside those blocks harbored genes encoding proteins involved in the vertebrate host-Plasmodium relationship undergoing faster evolution. Such genome architecture may have facilitated colonizing vertebrate hosts. Phylogenomic analyses estimated the common ancestor between P. vivax and an African ape parasite P. vivax-like, within the Asian nonhuman primates parasites clade. Time estimates incorporating P. gonderi placed the P. vivax and P. vivax-like common ancestor in the late Pleistocene, a time of active migration of hominids between Africa and Asia. Thus, phylogenomic and time-tree analyses are consistent with an Asian origin for P. vivax and an introduction of P. vivax-like into Africa. Unlike other studies, time estimates for the clade with Plasmodium falciparum, the most lethal human malaria parasite, coincide with their host species radiation, African hominids. Overall, the newly assembled genome presented here has the quality to support comparative genomic investigations in Plasmodium.

OMA orthology in 2024: improved prokaryote coverage, ancestral and extant GO enrichment, a revamped synteny viewer and more in the OMA Ecosystem

In this update paper, we present the latest developments in the OMA browser knowledgebase, which aims to provide high-quality orthology inferences and facilitate the study of gene families, genomes and their evolution. First, we discuss the addition of new species in the database, particularly an expanded representation of prokaryotic species. The OMA browser now offers Ancestral Genome pages and an Ancestral Gene Order viewer, allowing users to explore the evolutionary history and gene content of ancestral genomes. We also introduce a revamped Local Synteny Viewer to compare genomic neighborhoods across both extant and ancestral genomes. Hierarchical Orthologous Groups (HOGs) are now annotated with Gene Ontology annotations, and users can easily perform extant or ancestral GO enrichments. Finally, we recap new tools in the OMA Ecosystem, including OMAmer for proteome mapping, OMArk for proteome quality assessment, OMAMO for model organism selection and Read2Tree for phylogenetic species tree construction from reads. These new features provide exciting opportunities for orthology analysis and comparative genomics. OMA is accessible at https://omabrowser.org.

Evolution of the Spider Homeobox Gene Repertoire by Tandem and Whole Genome Duplication

Gene duplication generates new genetic material that can contribute to the evolution of gene regulatory networks and phenotypes. Duplicated genes can undergo subfunctionalization to partition ancestral functions and/or neofunctionalization to assume a new function. We previously found there had been a whole genome duplication (WGD) in an ancestor of arachnopulmonates, the lineage including spiders and scorpions but excluding other arachnids like mites, ticks, and harvestmen. This WGD was evidenced by many duplicated homeobox genes, including two Hox clusters, in spiders. However, it was unclear which homeobox paralogues originated by WGD versus smaller-scale events such as tandem duplications. Understanding this is a key to determining the contribution of the WGD to arachnopulmonate genome evolution. Here we characterized the distribution of duplicated homeobox genes across eight chromosome-level spider genomes. We found that most duplicated homeobox genes in spiders are consistent with an origin by WGD. We also found two copies of conserved homeobox gene clusters, including the Hox, NK, HRO, Irx, and SINE clusters, in all eight species. Consistently, we observed one copy of each cluster was degenerated in terms of gene content and organization while the other remained more intact. Focussing on the NK cluster, we found evidence for regulatory subfunctionalization between the duplicated NK genes in the spider Parasteatoda tepidariorum compared to their single-copy orthologues in the harvestman Phalangium opilio. Our study provides new insights into the relative contributions of multiple modes of duplication to the homeobox gene repertoire during the evolution of spiders and the function of NK genes.

Unraveling the complex evolutionary history of lepidopteran chromosomes through ancestral chromosome reconstruction and novel chromosome nomenclature

BACKGROUND

Lepidoptera is one of the most species-rich animal groups, with substantial karyotype variations among species due to chromosomal rearrangements. Knowledge of the evolutionary patterns of lepidopteran chromosomes still needs to be improved.

RESULTS

Here, we used chromosome-level genome assemblies of 185 lepidopteran insects to reconstruct an ancestral reference genome and proposed a new chromosome nomenclature. Thus, we renamed over 5000 extant chromosomes with this system, revealing the historical events of chromosomal rearrangements and their features. Additionally, our findings indicate that, compared with autosomes, the Z chromosome in Lepidoptera underwent a fast loss of conserved genes, rapid acquisition of lineage-specific genes, and a low rate of gene duplication. Moreover, we presented evidence that all available 67 W chromosomes originated from a common ancestor chromosome, with four neo-W chromosomes identified, including one generated by fusion with an autosome and three derived through horizontal gene transfer. We also detected nearly 4000 inter-chromosomal gene movement events. Notably, Geminin is transferred from the autosome to the Z chromosome. When located on the autosome, Geminin shows female-biased expression, but on the Z chromosome, it exhibits male-biased expression. This contributes to the sexual dimorphism of body size in silkworms.

CONCLUSIONS

Our study sheds light on the complex evolutionary history of lepidopteran chromosomes based on ancestral chromosome reconstruction and novel chromosome nomenclature.

New Challenges for Anatomists in the Era of Omics

Anatomic studies have traditionally relied on macroscopic, microscopic, and histological techniques to investigate the structure of tissues and organs. Anatomic studies are essential in many fields, including medicine, biology, and veterinary science. Advances in technology, such as imaging techniques and molecular biology, continue to provide new insights into the anatomy of living organisms. Therefore, anatomy remains an active and important area in the scientific field. The consolidation in recent years of some omics technologies such as genomics, transcriptomics, proteomics, and metabolomics allows for a more complete and detailed understanding of the structure and function of cells, tissues, and organs. These have been joined more recently by "omics" such as radiomics, pathomics, and connectomics, supported by computer-assisted technologies such as neural networks, 3D bioprinting, and artificial intelligence. All these new tools, although some are still in the early stages of development, have the potential to strongly contribute to the macroscopic and microscopic characterization in medicine. For anatomists, it is time to hitch a ride and get on board omics technologies to sail to new frontiers and to explore novel scenarios in anatomy.