Impact of gene gains, losses and duplication modes on the origin and diversification of vertebrates

Anciently duplicated genes continuously recruited to heart expression in vertebrate evolution are associated with heart chamber increase

Although gene/genome duplications in the early stage of vertebrates have been thought to provide major resources of raw genetic materials for evolutionary innovations, it is unclear whether they continuously contribute to the evolution of morphological complexity during the course of vertebrate evolution, such as the evolution from two heart chambers (fishes) to four heart chambers (mammals and birds). We addressed this issue by our heart RNA-Seq experiments combined with published data, using 13 vertebrates and one invertebrate (sea squirt, as an outgroup). Our evolutionary transcriptome analysis showed that number of ancient paralogous genes expressed in heart tends to increase with the increase of heart chamber number along the vertebrate phylogeny, in spite that most of them were duplicated at the time near to the origin of vertebrates or even more ancient. Moreover, those paralogs expressed in heart exert considerably different functions from heart-expressed singletons: the former are functionally enriched in cardiac muscle and muscle contraction-related categories, whereas the latter play more basic functions of energy generation like aerobic respiration. These findings together support the notion that recruiting anciently paralogous genes that are expressed in heart is associated with the increase of chamber number in vertebrate evolution.

Deep Conservation and Unexpected Evolutionary History of Neighboring lncRNAs MALAT1 and NEAT1

Long non-coding RNAs (lncRNAs) have begun to receive overdue attention for their regulatory roles in gene expression and other cellular processes. Although most lncRNAs are lowly expressed and tissue-specific, notable exceptions include MALAT1 and its genomic neighbor NEAT1, two highly and ubiquitously expressed oncogenes with roles in transcriptional regulation and RNA splicing. Previous studies have suggested that NEAT1 is found only in mammals, while MALAT1 is present in all gnathostomes (jawed vertebrates) except birds. Here we show that these assertions are incomplete, likely due to the challenges associated with properly identifying these two lncRNAs. Using phylogenetic analysis and structure-aware annotation of publicly available genomic and RNA-seq coverage data, we show that NEAT1 is a common feature of tetrapod genomes except birds and squamates. Conversely, we identify MALAT1 in representative species of all major gnathostome clades, including birds. Our in-depth examination of MALAT1, NEAT1, and their genomic context in a wide range of vertebrate species allows us to reconstruct the series of events that led to the formation of the locus containing these genes in taxa from cartilaginous fish to mammals. This evolutionary history includes the independent loss of NEAT1 in birds and squamates, since NEAT1 is found in the closest living relatives of both clades (crocodilians and tuataras, respectively). These data clarify the origins and relationships of MALAT1 and NEAT1 and highlight an opportunity to study the change and continuity in lncRNA structure and function over deep evolutionary time.

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.

The evolution of NLRC3 subfamily genes in Sebastidae teleost fishes

BACKGROUND

With more than 36,000 valid fish species, teleost fishes constitute the most species-rich vertebrate clade and exhibit extensive genetic and phenotypic variation, including diverse immune defense strategies. NLRC3 subfamily genes, which are specific to fishes, play vital roles in the immune system of teleosts. The evolution of teleosts has been impacted by several whole-genome duplication (WGD) events, which might be a key reason for the expansions of the NLRC3 subfamily, but detailed knowledge of NLRC3 subfamily evolution in the family Sebastidae is still limited.

RESULTS

Phylogenetic inference of NLRC3 subfamily protein sequences were conducted to evaluate the orthology of NLRC3 subfamily genes in black rockfish (Sebastes schlegilii), 13 other fish species from the families Sebastidae, Serranidae, Gasterosteidae and Cyclopteridae, and three species of high vertebrates (bird, reptile and amphibian). WGD analyses were used to estimate expansions and contractions of the NLRC3 subfamily, and patterns of expression of NLRC3 subfamily genes in black rockfish following bacterial infections were used to investigate the functional roles of these genes in the traditional and mucosal immune system of the Sebastidae. Different patterns of gene expansions and contractions were observed in 17 fish and other species examined, and one and two whole-genome duplication events were observed in two members of family Sebastidae (black rockfish and honeycomb rockfish, Sebastes umbrosus), respectively. Subsequently, 179 copy numbers of NLRC3 genes were found in black rockfish and 166 in honeycomb rockfish. Phylogenetic analyses corroborated the conservation and evolution of NLRC3 orthologues between Sebastidae and other fish species. Finally, differential expression analyses provided evidence of the immune roles of NLRC3 genes in black rockfish during bacterial infections and gene ontology analysis also indicated other functional roles.

CONCLUSIONS

We hypothesize that NLRC3 genes have evolved a variety of different functions, in addition to their role in the immune response, as a result of whole genome duplication events during teleost diversification. Importantly, this study had underscored the importance of sampling across taxonomic groups, to better understand the evolutionary patterns of the innate immunity system on which complex immunological novelties arose. Moreover, the results in this study could extend current knowledge of the plasticity of the immune system.

Modification of maternally defined H3K4me3 regulates the inviability of interspecific Xenopus hybrids

Increasing evidence suggests that interspecific hybridization is crucial to speciation. However, chromatin incompatibility during interspecific hybridization often renders this process. Genomic imbalances such as chromosomal DNA loss and rearrangements leading to infertility have been commonly noted in hybrids. The mechanism underlying reproductive isolation of interspecific hybridization remains elusive. Here, we identified that modification of maternally defined H3K4me3 in Xenopus laevis and Xenopus tropicalis hybrids determines the different fates of the two types of hybrids as te×ls with developmental arrest and viable le×ts. Transcriptomics highlighted that the P53 pathway was overactivated, and the Wnt signaling pathway was suppressed in te×ls hybrids. Moreover, the lack of maternal H3K4me3 in te×ls disturbed the balance of gene expression between the L and S subgenomes in this hybrid. Attenuation of p53 can postpone the arrested development of te×ls. Our study suggests an additional model of reproductive isolation based on modifications of maternally defined H3K4me3.

Genetic dissection of steroid-hormone modulated social behavior: Novel paralogous genes are a boon for discovery

Research across species has led to important discoveries on the functions of steroid hormones in the regulation of behavior. However, like in many fields, advancements in transgenic and mutagenic technology allowed mice to become the premier genetic model for conducting many experiments to understand how steroids control social behavior. Since there has been a general lack of parallel methodological developments in other species, many of the findings cannot be generalized. This is especially the case for teleost fish, in which a whole-genome duplication produced novel paralogs for key steroid hormone signaling genes. In this review, we summarize technical advancements over the history of the field of neuroendocrinology that have led to important insights in our understanding of the control of social behavior by steroids. We demonstrate that early mouse genetic models to understand these mechanisms suffered from several issues that were remedied by more precise transgenic technological advancements. We then highlight the importance of CRISPR/Cas9 gene editing tools that will in time bridge the gap between mice and non-traditional model species for understanding principles of steroid hormone action in the modulation of social behavior. We specifically highlight the role of teleost fish in bridging this gap because they are 1) highly genetically tractable and 2) provide a novel advantage in achieving precise genetic control. The field of neuroendocrinology is entering a new "gene editing revolution" that will lead to novel discoveries about the roles of steroid hormones in the regulation and evolutionary trajectories of social behavior.

Salmonidae Genome: Features, Evolutionary and Phylogenetic Characteristics

The salmon family is one of the most iconic and economically important fish families, primarily possessing meat of excellent taste as well as irreplaceable nutritional and biological value. One of the most common and, therefore, highly significant members of this family, the Atlantic salmon (Salmo salar L.), was not without reason one of the first fish species for which a high-quality reference genome assembly was produced and published. Genomic advancements are becoming increasingly essential in both the genetic enhancement of farmed salmon and the conservation of wild salmon stocks. The salmon genome has also played a significant role in influencing our comprehension of the evolutionary and functional ramifications of the ancestral whole-genome duplication event shared by all Salmonidae species. Here we provide an overview of the current state of research on the genomics and phylogeny of the various most studied subfamilies, genera, and individual salmonid species, focusing on those studies that aim to advance our understanding of salmonid ecology, physiology, and evolution, particularly for the purpose of improving aquaculture production. This review should make potential researchers pay attention to the current state of research on the salmonid genome, which should potentially attract interest in this important problem, and hence the application of new technologies (such as genome editing) in uncovering the genetic and evolutionary features of salmoniforms that underlie functional variation in traits of commercial and scientific importance.

Parallel evolution of amphioxus and vertebrate small-scale gene duplications

BACKGROUND

Amphioxus are non-vertebrate chordates characterized by a slow morphological and molecular evolution. They share the basic chordate body-plan and genome organization with vertebrates but lack their 2R whole-genome duplications and their developmental complexity. For these reasons, amphioxus are frequently used as an outgroup to study vertebrate genome evolution and Evo-Devo. Aside from whole-genome duplications, genes continuously duplicate on a smaller scale. Small-scale duplicated genes can be found in both amphioxus and vertebrate genomes, while only the vertebrate genomes have duplicated genes product of their 2R whole-genome duplications. Here, we explore the history of small-scale gene duplications in the amphioxus lineage and compare it to small- and large-scale gene duplication history in vertebrates.

RESULTS

We present a study of the European amphioxus (Branchiostoma lanceolatum) gene duplications thanks to a new, high-quality genome reference. We find that, despite its overall slow molecular evolution, the amphioxus lineage has had a history of small-scale duplications similar to the one observed in vertebrates. We find parallel gene duplication profiles between amphioxus and vertebrates and conserved functional constraints in gene duplication. Moreover, amphioxus gene duplicates show levels of expression and patterns of functional specialization similar to the ones observed in vertebrate duplicated genes. We also find strong conservation of gene synteny between two distant amphioxus species, B. lanceolatum and B. floridae, with two major chromosomal rearrangements.

CONCLUSIONS

In contrast to their slower molecular and morphological evolution, amphioxus' small-scale gene duplication history resembles that of the vertebrate lineage both in quantitative and in functional terms.

Diversification of the aquaporin family in geographical isolated oyster species promote the adaptability to dynamic environments

BACKGROUND

The diversified aquaporin (AQP) family that was derived from gene duplication and subsequent functional differentiation play critical roles in multiple physiological processes and in adaptation to the dynamic environments during the evolutionary process. Oysters are a group of bivalve fauna in Mollusca that were widely distributed around the world and show extraordinary adaptation to harsh environments. However, knowledge is lacking with the diversity and evolution of the AQP family in oysters, even in molluscs.

RESULTS

Here, we performed a comprehensive analysis of the AQP family in three geographical isolated oyster species that are native to different environments. Genome distribution and phylogenetic analysis revealed that the expansion of the AQP family in oysters were attributed to tandem duplication. Synteny analysis indicated that large-scale inversions lead to the independent duplication or deletion of the AQPs after speciation. As a consequence, these independent duplication events contributed to the diversification of the AQP family in different oysters. Pore pattern analysis suggested that the duplicated AQPs in oysters were highly diversified in inner surface profiles, implying the subsequent functional differentiation. The comparison conducted based on the transcriptome data demonstrated that the functional differentiated AQP family members in oysters may play critical roles in maintaining the balance between the stationary homeostasis and dynamic environments.

CONCLUSIONS

Our observation provides evidence for the correlation between the duplicated and functional differentiated AQP family and the adaptation to stationary life under dynamic environments in oysters. Additionally, it also broadens our knowledge of the evolution of AQP family in molluscs.

Amphioxus muscle transcriptomes reveal vertebrate-like myoblast fusion genes and a highly conserved role of insulin signalling in the metabolism of muscle

BACKGROUND

The formation and functioning of muscles are fundamental aspects of animal biology, and the evolution of 'muscle genes' is central to our understanding of this tissue. Feeding-fasting-refeeding experiments have been widely used to assess muscle cellular and metabolic responses to nutrition. Though these studies have focused on vertebrate models and only a few invertebrate systems, they have found similar processes are involved in muscle degradation and maintenance. Motivation for these studies stems from interest in diseases whose pathologies involve muscle atrophy, a symptom also triggered by fasting, as well as commercial interest in the muscle mass of animals kept for consumption. Experimentally modelling atrophy by manipulating nutritional state causes muscle mass to be depleted during starvation and replenished with refeeding so that the genetic mechanisms controlling muscle growth and degradation can be understood.

RESULTS

Using amphioxus, the earliest branching chordate lineage, we address the gap in previous work stemming from comparisons between distantly related vertebrate and invertebrate models. Our amphioxus feeding-fasting-refeeding muscle transcriptomes reveal a highly conserved myogenic program and that the pro-orthologues of many vertebrate myoblast fusion genes were present in the ancestral chordate, despite these invertebrate chordates having unfused mononucleate myocytes. We found that genes differentially expressed between fed and fasted amphioxus were orthologous to the genes that respond to nutritional state in vertebrates. This response is driven in a large part by the highly conserved IGF/Akt/FOXO pathway, where depleted nutrient levels result in activation of FOXO, a transcription factor with many autophagy-related gene targets.

CONCLUSION

Reconstruction of these gene networks and pathways in amphioxus muscle provides a key point of comparison between the distantly related groups assessed thus far, significantly refining the reconstruction of the ancestral state for chordate myoblast fusion genes and identifying the extensive role of duplicated genes in the IGF/Akt/FOXO pathway across animals. Our study elucidates the evolutionary trajectory of muscle genes as they relate to the increased complexity of vertebrate muscles and muscle development.

Duplication and subsequent functional diversification of aquaporin family in Pacific abalone Haliotis discus hannai

Aquaporins (AQPs) are a group of proteins that evolved to mediate specific permeation of water and other small solutes, playing important roles in osmoregulation and nutrition, especially for aquatic animals. Genome-wide characterization of the AQP family in a typical mollusc, Pacific abalone, suggested that tandem duplication and retroduplication led to the dramatic expansion and diversification of AQP genes. Structural analysis indicated that tandem duplicated AQPs showed abnormal characteristics. The conserved amino acids in the key site of the Ar/R region were replaced by the others. These substitutions altered the pore diameter and properties of the inner surface and could accommodate the pass through of other molecules except water. Functional analysis indicated that abnormal Ar/R region of the tandemly adjacent members led to the different permeability, suggesting the neofunctionalization of tandemly duplicated genes. Mutation analysis indicated that at the key site of Ar/R region, just a single amino acid substitute could alter the permeability of HdAQPs, further explaining the mechanism of neofunctionalization between the tandem duplicated HdAQPs. Our observations provided strong evidence that duplication and subsequent neofunctionalization have led to structural and functional diversity of AQPs in Pacific abalone, providing insights into the evolution of AQPs in molluscs.

MicroRNAs as Indicators into the Causes and Consequences of Whole-Genome Duplication Events

Whole-genome duplications (WGDs) have long been considered the causal mechanism underlying dramatic increases to morphological complexity due to the neo-functionalization of paralogs generated during these events. Nonetheless, an alternative hypothesis suggests that behind the retention of most paralogs is not neo-functionalization, but instead the degree of the inter-connectivity of the intended gene product, as well as the mode of the WGD itself. Here, we explore both the causes and consequences of WGD by examining the distribution, expression, and molecular evolution of microRNAs (miRNAs) in both gnathostome vertebrates as well as chelicerate arthropods. We find that although the number of miRNA paralogs tracks the number of WGDs experienced within the lineage, few of these paralogs experienced changes to the seed sequence, and thus are functionally equivalent relative to their mRNA targets. Nonetheless, in gnathostomes, although the retention of paralogs following the 1R autotetraploidization event is similar across the two subgenomes, the paralogs generated by the gnathostome 2R allotetraploidization event are retained in higher numbers on one subgenome relative to the second, with the miRNAs found on the preferred subgenome showing both higher expression of mature miRNA transcripts and slower molecular evolution of the precursor miRNA sequences. Importantly, WGDs do not result in the creation of miRNA novelty, nor do WGDs correlate to increases in complexity. Instead, it is the number of miRNA seed sequences in the genome itself that not only better correlate to instances in complexification, but also mechanistically explain why complexity increases when new miRNA families are established.

Evolution of the DAN gene family in vertebrates

The DAN gene family (DAN, Differential screening-selected gene Aberrant in Neuroblastoma) is a group of genes that is expressed during development and plays fundamental roles in limb bud formation and digitation, kidney formation and morphogenesis and left-right axis specification. During adulthood the expression of these genes are associated with diseases, including cancer. Although most of the attention to this group of genes has been dedicated to understanding its role in physiology and development, its evolutionary history remains poorly understood. Thus, the goal of this study is to investigate the evolutionary history of the DAN gene family in vertebrates, with the objective of complementing the already abundant physiological information with an evolutionary context. Our results recovered the monophyly of all DAN gene family members and divide them into five main groups. In addition to the well-known DAN genes, our phylogenetic results revealed the presence of two new DAN gene lineages; one is only retained in cephalochordates, whereas the other one (GREM3) was only identified in cartilaginous fish, holostean fish, and coelacanth. According to the phyletic distribution of the genes, the ancestor of gnathostomes possessed a repertoire of eight DAN genes, and during the radiation of the group GREM1, GREM2, SOST, SOSTDC1, and NBL1 were retained in all major groups, whereas, GREM3, CER1, and DAND5 were differentially lost.

Improved Understanding of the Role of Gene and Genome Duplications in Chordate Evolution With New Genome and Transcriptome Sequences

Comparative approaches to understanding chordate genomes have uncovered a significant role for gene duplications, including whole genome duplications (WGDs), giving rise to and expanding gene families. In developmental biology, gene families created and expanded by both tandem and WGDs are paramount. These genes, often involved in transcription and signalling, are candidates for underpinning major evolutionary transitions because they are particularly prone to retention and subfunctionalisation, neofunctionalisation, or specialisation following duplication. Under the subfunctionalisation model, duplication lays the foundation for the diversification of paralogues, especially in the context of gene regulation. Tandemly duplicated paralogues reside in the same regulatory environment, which may constrain them and result in a gene cluster with closely linked but subtly different expression patterns and functions. Ohnologues (WGD paralogues) often diversify by partitioning their expression domains between retained paralogues, amidst the many changes in the genome during rediploidisation, including chromosomal rearrangements and extensive gene losses. The patterns of these retentions and losses are still not fully understood, nor is the full extent of the impact of gene duplication on chordate evolution. The growing number of sequencing projects, genomic resources, transcriptomics, and improvements to genome assemblies for diverse chordates from non-model and under-sampled lineages like the coelacanth, as well as key lineages, such as amphioxus and lamprey, has allowed more informative comparisons within developmental gene families as well as revealing the extent of conserved synteny across whole genomes. This influx of data provides the tools necessary for phylogenetically informed comparative genomics, which will bring us closer to understanding the evolution of chordate body plan diversity and the changes underpinning the origin and diversification of vertebrates.

Transcriptomic analysis of gonadal development in parasitic and non-parasitic lampreys (Ichthyomyzon spp.), with a comparison of genomic resources in these non-model species

Lampreys are jawless fishes that diverged ∼550 million years ago from other vertebrates. Sequencing of the somatic and the germline genomes of the sea lamprey (Petromyzon marinus) in 2013 and 2018, respectively, has helped to improve our understanding of the genes and gene networks that control many aspects of lamprey development. However, little is known about the genetic basis of gonadal differentiation in lampreys, partly due to the prolonged period during which their gonads remain sexually indeterminate. We performed RNA-sequencing on gonadal samples from four chestnut lamprey (Ichthyomyzon castaneus) and six northern brook lamprey (I. fossor) to identify differentially expressed genes (DEG’s) and pathways associated with transcriptomic differences in: (1) larvae during early gonadal differentiation versus definitive females (i.e., with oocytes in the slow cytoplasmic growth phase); and (2) females versus definitive males undergoing spermatogonial proliferation. We compared the mapping percentages of these transcriptomes to the two available sea lamprey reference genomes and three annotation files (Ensembl and UCSC for the somatic genome and SIMRbase for the germline genome). We found that mapping the RNA-seq reads to the germline genome gave superior results and, using Trinotate, we provided new putative annotations for 8161 genes in the somatic assembly and 880 genes for the germline assembly. We identified >2000 DEG’s between stages and sexes, as well as biological pathways associated with each. Interestingly, some of the upregulated genes (e.g., DEG’s associated with spermiation) suggest that changes in gene expression can precede morphological changes by several months. In contrast, only 81 DEG’s were evident between the chestnut lamprey (that remains sexually immature during an extended post-metamorphic parasitic feeding phase) and the nonparasitic northern brook lamprey (that undergoes sexual maturation near the end of metamorphosis), but few replicates were available for comparable stages and sexes. This work lays the foundation for identifying and confirming the orthology and the function of genes involved in gonadal development in these and other lamprey species across more developmental stages.

The origin of the expressed retrotransposed gene ACTBL2 and its influence on human melanoma cells' motility and focal adhesion formation

We have recently found that β-actin-like protein 2 (actbl2) forms complexes with gelsolin in human melanoma cells and can polymerize. Phylogenetic and bioinformatic analyses showed that actbl2 has a common origin with two non-muscle actins, which share a separate history from the muscle actins. The actin groups' divergence started at the beginning of vertebrate evolution, and actbl2 actins are characterized by the largest number of non-conserved amino acid substitutions of all actins. We also discovered that ACTBL2 is expressed at a very low level in several melanoma cell lines, but a small subset of cells exhibited a high ACTBL2 expression. We found that clones with knocked-out ACTBL2 (CR-ACTBL2) or overexpressing actbl2 (OE-ACTBL2) differ from control cells in the invasion, focal adhesion formation, and actin polymerization ratio, as well as in the formation of lamellipodia and stress fibers. Thus, we postulate that actbl2 is the seventh actin isoform and is essential for cell motility.

ZP4 Is Present in Murine Zona Pellucida and Is Not Responsible for the Specific Gamete Interaction

Mammalian eggs are surrounded by an extracellular matrix called the zona pellucida (ZP). This envelope participates in processes such as acrosome reaction induction, sperm binding, protection of the oviductal embryo, and may be involved in speciation. In eutherian mammals, this coat is formed of three or four glycoproteins (ZP1-ZP4). While Mus musculus has been used as a model to study the ZP for more than 35 years, surprisingly, it is the only eutherian species in which the ZP is formed of three glycoproteins Zp1, Zp2, and Zp3, Zp4 being a pseudogene. Zp4 was lost in the Mus lineage after it diverged from Rattus, although it is not known when precisely this loss occurred. In this work, the status of Zp4 in several murine rodents was tested by phylogenetic, molecular, and proteomic analyses. Additionally, assays of cross in vitro fertilization between three and four ZP rodents were performed to test the effect of the presence of Zp4 in murine ZP and its possible involvement in reproductive isolation. Our results showed that Zp4 pseudogenization is restricted to the subgenus Mus, which diverged around 6 MYA. Heterologous in vitro fertilization assays demonstrate that a ZP formed of four glycoproteins is not a barrier for the spermatozoa of species with a ZP formed of three glycoproteins. This study identifies the existence of several mouse species with four ZPs that can be considered suitable for use as an experimental animal model to understand the structural and functional roles of the four ZP proteins in other species, including human.

Unconventional Actions of Glycoprotein Hormone Subunits: A Comprehensive Review

The glycoprotein hormones (GPH) are heterodimers composed of a common α subunit and a specific β subunit. They act by activating specific leucine-rich repeat G protein-coupled receptors. However, individual subunits have been shown to elicit responses in cells devoid of the receptor for the dimeric hormones. The α subunit is involved in prolactin production from different tissues. The human chorionic gonadotropin β subunit (βhCG) plays determinant roles in placentation and in cancer development and metastasis. A truncated form of the thyrotropin (TSH) β subunit is also reported to have biological effects. The GPH α- and β subunits are derived from precursor genes (gpa and gpb, respectively), which are expressed in most invertebrate species and are still represented in vertebrates as GPH subunit paralogs (gpa2 and gpb5, respectively). No specific receptor has been found for the vertebrate GPA2 and GPB5 even if their heterodimeric form is able to activate the TSH receptor in mammals. Interestingly, GPA and GPB are phylogenetically and structurally related to cysteine-knot growth factors (CKGF) and particularly to a group of antagonists that act independently on any receptor. This review article summarizes the observed actions of individual GPH subunits and presents the current hypotheses of how these actions might be induced. New approaches are also proposed in light of the evolutionary relatedness with antagonists of the CKGF family of proteins.

A tale of two leeches: Toward the understanding of the evolution and development of behavioral neural circuits

In the animal kingdom, behavioral traits encompass a broad spectrum of biological phenotypes that have critical roles in adaptive evolution, but an EvoDevo approach has not been broadly used to study behavior evolution. Here, we propose that, by integrating two leech model systems, each of which has already attained some success in its respective field, it is possible to take on behavioral traits with an EvoDevo approach. We first identify the developmental changes that may theoretically lead to behavioral evolution and explain why an EvoDevo study of behavior is challenging. Next, we discuss the pros and cons of the two leech model species, Hirudo, a classic model for invertebrate neurobiology, and Helobdella, an emerging model for clitellate developmental biology, as models for behavioral EvoDevo research. Given the limitations of each leech system, neither is particularly strong for behavioral EvoDevo. However, the two leech systems are complementary in their technical accessibilities, and they do exhibit some behavioral similarities and differences. By studying them in parallel and together with additional leech species such as Haementeria, it is possible to explore the different levels of behavioral development and evolution.

Genomic signatures of globally enhanced gene duplicate accumulation in the megadiverse higher Diptera fueling intralocus sexual conflict resolution

Gene duplication is an important source of evolutionary innovation. To explore the relative impact of gene duplication during the diversification of major insect model system lineages, we performed a comparative analysis of lineage-specific gene duplications in the fruit fly Drosophila melanogaster (Diptera: Brachycera), the mosquito Anopheles gambiae (Diptera: Culicomorpha), the red flour beetle Tribolium castaneum (Coleoptera), and the honeybee Apis mellifera (Hymenoptera). Focusing on close to 6,000 insect core gene families containing maximally six paralogs, we detected a conspicuously higher number of lineage-specific duplications in Drosophila (689) compared to Anopheles (315), Tribolium (386), and Apis (223). Based on analyses of sequence divergence, phylogenetic distribution, and gene ontology information, we present evidence that an increased background rate of gene duplicate accumulation played an exceptional role during the diversification of the higher Diptera (Brachycera), in part by providing enriched opportunities for intralocus sexual conflict resolution, which may have boosted speciation rates during the early radiation of the megadiverse brachyceran subclade Schizophora.

Ancient Genomic Regulatory Blocks Are a Source for Regulatory Gene Deserts in Vertebrates after Whole-Genome Duplications

We investigated how the two rounds of whole-genome duplication that occurred at the base of the vertebrate lineage have impacted ancient microsyntenic associations involving developmental regulators (known as genomic regulatory blocks, GRBs). We showed that the majority of GRBs identified in the last common ancestor of chordates have been maintained as a single copy in humans. We found evidence that dismantling of the duplicated GRB copies occurred early in vertebrate evolution often through the differential retention of the regulatory gene but loss of the bystander gene’s exonic sequences. Despite the large evolutionary scale, the presence of duplicated highly conserved noncoding regions provided unambiguous proof for this scenario for multiple ancient GRBs. Remarkably, the dismantling of ancient GRB duplicates has contributed to the creation of large gene deserts associated with regulatory genes in vertebrates, providing a potentially widespread mechanism for the origin of these enigmatic genomic traits.

New group of transmembrane proteins associated with desiccation tolerance in the anhydrobiotic midge Polypedilum vanderplanki

Larvae of the sleeping chironomid Polypedilum vanderplanki are known for their extraordinary ability to survive complete desiccation in an ametabolic state called "anhydrobiosis". The unique feature of P. vanderplanki genome is the presence of expanded gene clusters associated with anhydrobiosis. While several such clusters represent orthologues of known genes, there is a distinct set of genes unique for P. vanderplanki. These include Lea-Island-Located (LIL) genes with no known orthologues except two of LEA genes of P. vanderplanki, PvLea1 and PvLea3. However, PvLIL proteins lack typical features of LEA such as the state of intrinsic disorder, hydrophilicity and characteristic LEA_4 motif. They possess four to five transmembrane domains each and we confirmed membrane targeting for three PvLILs. Conserved amino acids in PvLIL are located in transmembrane domains or nearby. PvLEA1 and PvLEA3 proteins are chimeras combining LEA-like parts and transmembrane domains, shared with PvLIL proteins. We have found that PvLil genes are highly upregulated during anhydrobiosis induction both in larvae of P. vanderplanki and P. vanderplanki-derived cultured cell line, Pv11. Thus, PvLil are a new intriguing group of genes that are likely to be associated with anhydrobiosis due to their common origin with some LEA genes and their induction during anhydrobiosis.

Origin and Evolution of Two Independently Duplicated Genes Encoding UDP- Glucose: Glycoprotein Glucosyltransferases in Caenorhabditis and Vertebrates

UDP- glucose: glycoprotein glucosyltransferase (UGGT) is a protein that operates as the gatekeeper for the endoplasmic reticulum (ER) quality control mechanism of glycoprotein folding. It is known that vertebrates and Caenorhabditis genomes harbor two uggt gene copies that exhibit differences in their properties.

Bayesian phylogenetic inference based on 195 UGGT and UGGT-like protein sequences of an ample spectrum of eukaryotic species showed that uggt genes went through independent duplications in Caenorhabditis and vertebrates. In both lineages, the catalytic domain of the duplicated genes was subjected to a strong purifying selective pressure, while the recognition domain was subjected to episodic positive diversifying selection. Selective relaxation in the recognition domain was more pronounced in Caenorhabditis uggt-b than in vertebrates uggt-2. Structural bioinformatics analysis revealed that Caenorhabditis UGGT-b protein lacks essential sequences proposed to be involved in the recognition of unfolded proteins. When we assayed glucosyltrasferase activity of a chimeric protein composed by Caenorhabditis uggt-b recognition domain fused to S. pombe catalytic domain expressed in yeast, no activity was detected.

The present results support the conservation of the UGGT activity in the catalytic domain and a putative divergent function of the recognition domain for the UGGT2 protein in vertebrates, which would have gone through a specialization process. In Caenorhabditis, uggt-b evolved under different constraints compared to uggt-a which, by means of a putative neofunctionalization process, resulted in a non-redundant paralog. The non-canonical function of uggt-b in the worm lineage highlights the need to take precautions before generalizing gene functions in model organisms.

Expansion of fish CCL20_like chemokines by genome and local gene duplication: Characterisation and expression analysis of 10 CCL20_like chemokines in rainbow trout (Oncorhynchus mykiss)

Mammalian CCL20, or macrophage inflammatory protein-3α, can function as a homeostatic and inflammatory chemokine. In relation to the latter, it is responsible for the chemoattraction of lymphocytes and dendritic cells to mucosal immune sites under inflammatory and pathological conditions. CK1, CK8A and CK8B are rainbow trout (Oncorhynchus mykiss) CC chemokines that were reported previously to be phylogenetically related to mammalian CCL20. In the current study, an additional seven CCL20_L paralogues in rainbow trout are reported, that are divided into three subgroups and have been designated here as: CCL20_L1a (also referred to as CK1), CCL20_L1b1-2, CCL20_L2a (CK8A), CCL20_L2b (CK8B), CCL20_L3a, and CCL20_L3b1-4. Multiple CCL20_L genes were also identified in other salmonids that arose from both whole genome duplication and local gene duplication. Phylogenetic tree, homology and synteny analysis support that CCL20_L1-3 found in salmonids are also present in most teleosts arose from the 3 R whole genome duplication and in some species, local gene duplication. Like mammalian CCL20, rainbow trout CCL20_L molecules possess a high positive net charge with a pI of 9.34-10.16, that is reported to be important for antimicrobial activity. Rainbow trout CCL20_L paralogues are differentially expressed and in general highly expressed in mucosal tissues, such as gills, thymus and intestine. The expression levels of rainbow trout CCL20_L paralogues are increased during development and following PAMP/cytokine stimulation. For example, in RTS-11 cells CCL20_L3b1 and CCL20_L3b2 are highly up-regulated by LPS, Poly I:C, recombinant(r) IFNa and rIL-1β. Trout CCL20_L paralogues are also increased after Yersinia ruckeri infection or Poly I:C stimulation in vivo, with CCL20_L3b1 and CCL20_L3b2 again highly up-regulated. Overall, this is the first report of the complete CCL20 chemokine subfamily in rainbow trout, and the analysis of their expression and modulation in vitro and in vivo. These results suggest that teleosts possess divergent CCL20_L molecules that may have important roles in anti-viral/anti-bacterial defence and in mucosal immunity.

Vertebrate Alpha2,8-Sialyltransferases (ST8Sia): A Teleost Perspective

We identified and analyzed α2,8-sialyltransferases sequences among 71 ray-finned fish species to provide the first comprehensive view of the Teleost ST8Sia repertoire. This repertoire expanded over the course of Vertebrate evolution and was primarily shaped by the whole genome events R1 and R2, but not by the Teleost-specific R3. We showed that duplicated st8sia genes like st8sia7, st8sia8, and st8sia9 have disappeared from Tetrapods, whereas their orthologues were maintained in Teleosts. Furthermore, several fish species specific genome duplications account for the presence of multiple poly-α2,8-sialyltransferases in the Salmonidae (ST8Sia II-r1 and ST8Sia II-r2) and in Cyprinuscarpio (ST8Sia IV-r1 and ST8Sia IV-r2). Paralogy and synteny analyses provided more relevant and solid information that enabled us to reconstruct the evolutionary history of st8sia genes in fish genomes. Our data also indicated that, while the mammalian ST8Sia family is comprised of six subfamilies forming di-, oligo-, or polymers of α2,8-linked sialic acids, the fish ST8Sia family, amounting to a total of 10 genes in fish, appears to be much more diverse and shows a patchy distribution among fish species. A focus on Salmonidae showed that (i) the two copies of st8sia2 genes have overall contrasted tissue-specific expressions, with noticeable changes when compared with human co-orthologue, and that (ii) st8sia4 is weakly expressed. Multiple sequence alignments enabled us to detect changes in the conserved polysialyltransferase domain (PSTD) of the fish sequences that could account for variable enzymatic activities. These data provide the bases for further functional studies using recombinant enzymes.

The evolutionary landscape of the Rab family in chordates

Intracellular traffic amongst organelles represents a key feature for eukaryotes and is orchestrated principally by members of Rab family, the largest within Ras superfamily. Given that variations in Rab repertoire have been fundamental in animal diversification, we provided the most exhaustive survey regarding the Rab toolkit of chordates. Our findings reveal the existence of 42 metazoan conserved subfamilies exhibiting a univocal intron/exon structure preserved from cnidarians to vertebrates. Since the current view does not capture the Rab complexity, we propose a new Rab family classification in three distinct monophyletic clades. The Rab complement of chordates shows a dramatic diversification due to genome duplications and independent gene duplications and losses with sharp differences amongst cephalochordates, tunicates and gnathostome vertebrates. Strikingly, the analysis of the domain architecture of this family highlighted the existence of chimeric calcium-binding Rabs, which are animal novelties characterized by a complex evolutionary history in gnathostomes and whose role in cellular metabolism is obscure. This work provides novel insights in the knowledge of Rab family: our hypothesis is that chordates represent a hotspot of Rab variability, with many events of gene gains and losses impacting intracellular traffic capabilities. Our results help to elucidate the role of Rab members in the transport amongst endomembranes and shed light on intracellular traffic routes in vertebrates. Then, since the predominant role of Rabs in the molecular communication between different cellular districts, this study paves to way to comprehend inherited or acquired human disorders provoked by dysfunctions in Rab genes.

Inadvertent Paralog Inclusion Drives Artifactual Topologies and Timetree Estimates in Phylogenomics

Increasingly, large phylogenomic data sets include transcriptomic data from nonmodel organisms. This not only has allowed controversial and unexplored evolutionary relationships in the tree of life to be addressed but also increases the risk of inadvertent inclusion of paralogs in the analysis. Although this may be expected to result in decreased phylogenetic support, it is not clear if it could also drive highly supported artifactual relationships. Many groups, including the hyperdiverse Lissamphibia, are especially susceptible to these issues due to ancient gene duplication events and small numbers of sequenced genomes and because transcriptomes are increasingly applied to resolve historically conflicting taxonomic hypotheses. We tested the potential impact of paralog inclusion on the topologies and timetree estimates of the Lissamphibia using published and de novo sequencing data including 18 amphibian species, from which 2,656 single-copy gene families were identified. A novel paralog filtering approach resulted in four differently curated data sets, which were used for phylogenetic reconstructions using Bayesian inference, maximum likelihood, and quartet-based supertrees. We found that paralogs drive strongly supported conflicting hypotheses within the Lissamphibia (Batrachia and Procera) and older divergence time estimates even within groups where no variation in topology was observed. All investigated methods, except Bayesian inference with the CAT-GTR model, were found to be sensitive to paralogs, but with filtering convergence to the same answer (Batrachia) was observed. This is the first large-scale study to address the impact of orthology selection using transcriptomic data and emphasizes the importance of quality over quantity particularly for understanding relationships of poorly sampled taxa.

De novo European eel transcriptome provides insights into the evolutionary history of duplicated genes in teleost lineages

Paralogues pairs are more frequently observed in eels (Anguilla sp.) than in other teleosts. The paralogues often show low phylogenetic distances; however, they have been assigned to the third round of whole genome duplication (WGD), shared by all teleosts (3R), due to their conserved synteny. The apparent contradiction of low phylogenetic difference and 3R conserved synteny led us to study the duplicated gene complement of the freshwater eels. With this aim, we assembled de novo transcriptomes of two highly relevant freshwater eel species: The European (Anguilla anguilla) and the Japanese eel (Anguilla japonica). The duplicated gene complement was analysed in these transcriptomes, and in the genomes and transcriptomes of other Actinopterygii species. The study included an assessment of neutral genetic divergence (4dTv), synteny, and the phylogenetic origins and relationships of the duplicated gene complements. The analyses indicated a high accumulation of duplications (1217 paralogue pairs) among freshwater eel genes, which may have originated in a WGD event after the Elopomorpha lineage diverged from the remaining teleosts, and thus not at the 3R. However, very similar results were observed in the basal Osteoglossomorpha and Clupeocephala branches, indicating that the specific genomic regions of these paralogues may still have been under tetrasomic inheritance at the split of the teleost lineages. Therefore, two potential hypotheses may explain the results: i) The freshwater eel lineage experienced an additional WGD to 3R, and ii) Some duplicated genomic regions experienced lineage specific rediploidization after 3R in the ancestor to freshwater eels. The supporting/opposing evidence for both hypotheses is discussed.

Japanese medaka as a model for studying the relaxin family genes involved in neuroendocrine regulation: Insights from the expression of fish-specific rln3 and insl5 and rxfp3/4-type receptor paralogues

The goal of this paper is to establish Japanese medaka (Oryzias latipes) as a model for relaxin family peptide research, particularly for studying the functions of RLN3 and INSL5, hormones playing roles in neuroendocrine regulation. Medaka, like other teleosts, retained duplicate copies of rln3, insl5 and their rxfp3/4-type receptors following fish-specific whole genome duplication (WGD) and paralogous copies of these genes may have sub-functionalised providing an intuitive model for teasing apart the pleiotropic roles of the corresponding genes in mammals. To this end, we provide experimental evidence for the expression of the relaxin family genes in medaka that had previously only been identified in-silico, confirm the gene structure of five of the ligand genes, characterise gene expression across multiple tissues and during embryonic development, perform in situ hybridization with anti-sense insl5a on embryos and in adult brain and intestinal samples, and compare these results to the data available in zebrafish. We find broad similarities but also some differences in the expression of relaxin family genes in zebrafish versus medaka, and find support for the hypothesis that the rln3a/rln3b and insl5a/insl5b paralogues have been subfunctionalized. Given that medaka has a suite of relaxin family genes more similar to other teleosts, and has retained the gene for rxfp4 (which is lost in zebrafish), our results suggest that O. latipes may be a good model for delineating the ancestral function of the relaxin family genes involved in neuroendocrine regulation.

A Likely Ancient Genome Duplication in the Speciose Reef-Building Coral Genus, Acropora

Whole-genome duplication (WGD) has been recognized as a significant evolutionary force in the origin and diversification of multiple organisms. Acropora, a speciose reef-building coral genus, is suspected to have originated by polyploidy. Yet, there is no genetic evidence to support this hypothesis. Using comprehensive phylogenomic and comparative genomic approaches, we analyzed six Acroporid genomes and found that a WGD event likely occurred ∼31 million years ago in the most recent common ancestor of Acropora, concurrent with a worldwide coral extinction. We found that duplicated genes were highly enriched in gene regulation functions, including those of stress responses. The functional clusters of duplicated genes are related to the divergence of gene expression patterns during development. Some proteinaceous toxins were generated by WGD in Acropora compared with other cnidarian species. Collectively, this study provides evidence for an ancient WGD event in corals, which helps explain the origin and diversification of Acropora.

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An ancient genome duplication occurred in the most recent common ancestor of Acropora

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This WGD event likely occurred between 28 and 36 mya in Acropora

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The WGD event potentially contributes to the origin and diversification of Acropora

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Duplications of toxic proteins were found in Acropora following the WGD

Oikopleura dioica: An Emergent Chordate Model to Study the Impact of Gene Loss on the Evolution of the Mechanisms of Development

The urochordate Oikopleura dioica is emerging as a nonclassical animal model in the field of evolutionary developmental biology (a.k.a. evo-devo) especially attractive for investigating the impact of gene loss on the evolution of mechanisms of development. This is because this organism fulfills the requirements of an animal model (i.e., has a simple and accessible morphology, a short generation time and life span, and affordable culture in the laboratory and amenable experimental manipulation), but also because O. dioica occupies a key phylogenetic position to understand the diversification and origin of our own phylum, the chordates. During its evolution, O. dioica genome has suffered a drastic process of compaction, becoming the smallest known chordate genome, a process that has been accompanied by exacerbating amount of gene losses. Interestingly, however, despite the extensive gene losses, including entire regulatory pathways essential for the embryonic development of other chordates, O. dioica retains the typical chordate body plan. This unexpected situation led to the formulation of the so-called inverse paradox of evo-devo, that is, when a genetic diversity is able to maintain a phenotypic unity. This chapter reviews the biological features of O. dioica as a model animal, along with the current data on the evolution of its genes and genome. We pay special attention to the numerous examples of gene losses that have taken place during the evolution of this unique animal model, which is helping us to understand to which the limits of evo-devo can be pushed off.

Diatom bloom-derived biotoxins cause aberrant development and gene expression in the appendicularian chordate Oikopleura dioica

Investigating environmental hazards than could affect appendicularians is of prime ecological interest because they are among the most abundant components of the mesozooplankton. This work shows that embryo development of the appendicularian Oikopleura dioica is compromised by diatom bloom-derived biotoxins, even at concentrations in the same range as those measured after blooms. Developmental gene expression analysis of biotoxin-treated embryos uncovers an aberrant golf ball-like phenotype affecting morphogenesis, midline convergence, and tail elongation. Biotoxins induce a rapid upregulation of defensome genes, and considerable delay and silencing of zygotic transcription of developmental genes. Upon a possible future intensification of blooms associated with ocean warming and acidification, our work puts an alert on the potential impact that an increase of biotoxins may have on marine food webs, and points to defensome genes as molecular biosensors that marine ecologists could use to monitor the genetic stress of natural populations exposed to microalgal blooms.

Wnt evolution and function shuffling in liberal and conservative chordate genomes

BACKGROUND

What impact gene loss has on the evolution of developmental processes, and how function shuffling has affected retained genes driving essential biological processes, remain open questions in the fields of genome evolution and EvoDevo. To investigate these problems, we have analyzed the evolution of the Wnt ligand repertoire in the chordate phylum as a case study.

RESULTS

We conduct an exhaustive survey of Wnt genes in genomic databases, identifying 156 Wnt genes in 13 non-vertebrate chordates. This represents the most complete Wnt gene catalog of the chordate subphyla and has allowed us to resolve previous ambiguities about the orthology of many Wnt genes, including the identification of WntA for the first time in chordates. Moreover, we create the first complete expression atlas for the Wnt family during amphioxus development, providing a useful resource to investigate the evolution of Wnt expression throughout the radiation of chordates.

CONCLUSIONS

Our data underscore extraordinary genomic stasis in cephalochordates, which contrasts with the liberal and dynamic evolutionary patterns of gene loss and duplication in urochordate genomes. Our analysis has allowed us to infer ancestral Wnt functions shared among all chordates, several cases of function shuffling among Wnt paralogs, as well as unique expression domains for Wnt genes that likely reflect functional innovations in each chordate lineage. Finally, we propose a potential relationship between the evolution of WntA and the evolution of the mouth in chordates.

Evolutionary and Expression Analyses Show Co-option of khdrbs Genes for Origin of Vertebrate Brain

Genes generated by whole genome duplications (WGD) can be co-opted by changing their regulation process or altering their coding proteins, which has been shown contributable to the emergence of vertebrate morphological novelties such as vertebrate cartilage. Mouse khdrbs genes, differing from its invertebrate orthologs, were mainly expressed in brain, hinting that khdrbs gene family as a member of genetic toolkit may be linked to vertebrate brain development. However, the evolutionary relationship between khdrbs gene family and vertebrate brain development is unclear. First, we analyzed the evolutionary history of khdrbs gene family in metazoans, and then investigated their expression patterns during early development and in adulthood of zebrafish. We found that the duplication of khdrbs gene family by WGD took place in zebrafish, and all zebrafish khdrbs genes were predominantly expressed in the substructures of brain during early development. Given the expression of invertebrate khdrbs gene in germ line, the distinct expression domains of zebrafish khdrbs genes in brain suggested that the duplicated khdrbs genes are co-opted for promoting the evolutionary origin of vertebrate brain.

Evolvability of the vertebrate craniofacial skeleton

The skull is a vertebrate novelty. Morphological adaptations of the skull are associated with major evolutionary transitions, including the shift to a predatory lifestyle and the ability to masticate while breathing. These adaptations include the chondrocranium, dermatocranium, articulated jaws, primary and secondary palates, internal choanae, the middle ear, and temporomandibular joint. The incredible adaptive diversity of the vertebrate skull indicates an underlying bauplan that promotes evolvability. Comparative studies in craniofacial development suggest that the craniofacial bauplan includes three secondary organizers, two that are bilaterally placed at the Hinge of the developing jaw, and one situated in the midline of the developing face (the FEZ). These organizers regulate tissue interactions between the cranial neural crest, the neuroepithelium, and facial and pharyngeal epithelia that regulate the development and evolvability of the craniofacial skeleton.

Evolution of the vertebrate insulin receptor substrate (Irs) gene family

BACKGROUND

Insulin receptor substrate (Irs) proteins are essential for insulin signaling as they allow downstream effectors to dock with, and be activated by, the insulin receptor. A family of four Irs proteins have been identified in mice, however the gene for one of these, IRS3, has been pseudogenized in humans. While it is known that the Irs gene family originated in vertebrates, it is not known when it originated and which members are most closely related to each other. A better understanding of the evolution of Irs genes and proteins should provide insight into the regulation of metabolism by insulin.

RESULTS

Multiple genes for Irs proteins were identified in a wide variety of vertebrate species. Phylogenetic and genomic neighborhood analyses indicate that this gene family originated very early in vertebrae evolution. Most Irs genes were duplicated and retained in fish after the fish-specific genome duplication. Irs genes have been lost of various lineages, including Irs3 in primates and birds and Irs1 in most fish. Irs3 and Irs4 experienced an episode of more rapid protein sequence evolution on the ancestral mammalian lineage. Comparisons of the conservation of the proteins sequences among Irs paralogs show that domains involved in binding to the plasma membrane and insulin receptors are most strongly conserved, while divergence has occurred in sequences involved in interacting with downstream effector proteins.

CONCLUSIONS

The Irs gene family originated very early in vertebrate evolution, likely through genome duplications, and in parallel with duplications of other components of the insulin signaling pathway, including insulin and the insulin receptor. While the N-terminal sequences of these proteins are conserved among the paralogs, changes in the C-terminal sequences likely allowed changes in biological function.

Co-accumulation of cis-regulatory and coding mutations during the pseudogenization of the Xenopus laevis homoeologs six6.L and six6.S

Common models for the evolution of duplicated genes after genome duplication are subfunctionalization, neofunctionalization, and pseudogenization. Although the crucial roles of cis-regulatory mutations in subfunctionalization are well-documented, their involvement in pseudogenization and/or neofunctionalization remains unclear. We addressed this issue by investigating the evolution of duplicated homeobox genes, six6.L and six6.S, in the allotetraploid frog Xenopus laevis. Based on a comparative expression analysis, we observed similar eye-specific expression patterns for the two loci and their single ortholog in the ancestral-type diploid species Xenopus tropicalis. However, we detected lower levels of six6.S expression than six6.L expression. The six6.S enhancer sequence was more highly diverged from the orthologous enhancer of X. tropicalis than the six6.L enhancer, and showed weaker activity in a transgenic reporter assay. Based on a phylogenetic analysis of the protein sequences, we observed greater divergence between X. tropicalis Six6 and Six6.S than between X. tropicalis Six6 and Six6.L, and the observed mutations were reminiscent of a microphthalmia mutation in human SIX6. Misexpression experiments showed that six6.S has weaker eye-enlarging activity than six6.L, and targeted disruption of six6.L reduced the eye size more significantly than that of six6.S. These results suggest that enhancer attenuation stimulates the accumulation of hypomorphic coding mutations, or vice versa, in one duplicated gene copy and facilitates pseudogenization. We also underscore the value of the allotetraploid genome of X. laevis as a resource for studying latent pathogenic mutations.

Diversity as Opportunity: Insights from 600 Million Years of AHR Evolution

The aryl hydrocarbon receptor (AHR) was for many years of interest only to pharmacologists and toxicologists. However, this protein has fundamental roles in biology that are being revealed through studies in diverse animal species. The AHR is an ancient protein. AHR homologs exist in most major groups of modern bilaterian animals, including deuterostomes (chordates, hemichordates, echinoderms) and the two major clades of protostome invertebrates [ecdysozoans (e.g. arthropods and nematodes) and lophotrochozoans (e.g. molluscs and annelids)]. AHR homologs also have been identified in cnidarians such as the sea anemone Nematostella and in the genome of Trichoplax, a placozoan. Bilaterians, cnidarians, and placozoans form the clade Eumetazoa, whose last common ancestor lived approximately 600 million years ago (MYA). The presence of AHR homologs in modern representatives of all these groups indicates that the original eumetazoan animal possessed an AHR homolog. Studies in invertebrates and vertebrates reveal parallel functions of AHR in the development and function of sensory neural systems, suggesting that these may be ancestral roles. Vertebrate animals are characterized by the expansion and diversification of AHRs, via gene and genome duplications, from the ancestral protoAHR into at least five classes of AHR-like proteins: AHR, AHR1, AHR2, AHR3, and AHRR. The evolution of multiple AHRs in vertebrates coincided with the acquisition of high-affinity binding of halogenated and polynuclear aromatic hydrocarbons and the emergence of adaptive functions involving regulation of xenobiotic-metabolizing enzymes and roles in adaptive immunity. The existence of multiple AHRs may have facilitated subfunction partitioning and specialization of specific AHR types in some taxa. Additional research in diverse model and non-model species will continue to enrich our understanding of AHR and its pleiotropic roles in biology and toxicology.

The Evolutionary Relationship between Alternative Splicing and Gene Duplication

The protein diversity that exists today has resulted from various evolutionary processes. It is well known that gene duplication (GD) along with the accumulation of mutations are responsible, among other factors, for an increase in the number of different proteins. The gene structure in eukaryotes requires the removal of non-coding sequences, introns, to produce mature mRNAs. This process, known as cis-splicing, referred to here as splicing, is regulated by several factors which can lead to numerous splicing arrangements, commonly designated as alternative splicing (AS). AS, producing several transcripts isoforms form a single gene, also increases the protein diversity. However, the evolution and manner for increasing protein variation differs between AS and GD. An important question is how are patterns of AS affected after a GD event. Here, we review the current knowledge of AS and GD, focusing on their evolutionary relationship. These two processes are now considered the main contributors to the increasing protein diversity and therefore their relationship is a relevant, yet understudied, area of evolutionary study.

Increased rates of protein evolution and asymmetric deceleration after the whole-genome duplication in yeasts

Background

Whole-genome duplication (WGD) events have shaped the genomes of eukaryotic organisms. Relaxed selection after duplication along with inherent functional constraints are thought to determine the fate of the paralogs and, ultimately, the evolution of gene function. Here, we investigated the rate of protein evolution (as measured by dN/dS ratios) before and after the WGD in the hemiascomycete yeasts, and the way in which changes in such rates relate to molecular and biological function.

Results

For most groups of orthologous genes (81%) we observed a change in the rates of evolution after genome duplication. Genes with atypically-low dN/dS ratio before the WGD were prone to increase their rates of evolution after duplication. Importantly, the paralogs were often different in their rates of evolution after the WGD (50% cases), however, this was more consistent with an asymmetric deceleration in the protein-evolution rates, rather than an asymmetric increase of the initial rates. Functional-category analysis showed that regulatory proteins such as protein kinases and transcription factors were enriched in genes that increase their rates of evolution after the WGD. While changes in the rate of protein-sequence evolution were associated to protein abundance, content of disordered regions, and contribution to fitness, these features were an attribute of specific functional classes.

Conclusions

Our results indicate that strong purifying selection in ancestral pre-duplication sequences is a strong predictor of increased rates after the duplication in yeasts and that asymmetry in evolution rate is established during the deceleration phase. In addition, changes in the rates at which paralogous sequences evolve before and after WGD are different for specific protein functions; increased rates of protein evolution after duplication occur preferentially in specific protein functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-017-0895-1) contains supplementary material, which is available to authorized users.

An Evolutionary Framework for Carpel Developmental Control Genes

Carpels are the female reproductive organs of flowering plants (angiosperms), enclose the ovules, and develop into fruits. The presence of carpels unites angiosperms, and they are suggested to be the most important autapomorphy of the angiosperms, e.g., they prevent inbreeding and allow efficient seed dispersal. Many transcriptional regulators and coregulators essential for carpel development are encoded by diverse gene families and well characterized in Arabidopsis thaliana. Among these regulators are AGAMOUS (AG), ETTIN (ETT), LEUNIG (LUG), SEUSS (SEU), SHORT INTERNODE/STYLISH (SHI/STY), and SEPALLATA1, 2, 3, 4 (SEP1, 2, 3, 4). However, the timing of the origin and their subsequent molecular evolution of these carpel developmental regulators are largely unknown. Here, we have sampled homologs of these carpel developmental regulators from the sequenced genomes of a wide taxonomic sampling of the land plants, such as Physcomitrella patens, Selaginella moellendorfii, Picea abies, and several angiosperms. Careful phylogenetic analyses were carried out that provide a phylogenetic background for the different gene families and provide minimal estimates for the ages of these developmental regulators. Our analyses and published work show that LUG-, SEU-, and SHI/STY-like genes were already present in the Most Recent Common Ancestor (MRCA) of all land plants, AG- and SEP-like genes were present in the MRCA of seed plants and their origin may coincide with the ξ Whole Genome Duplication. Our work shows that the carpel development regulatory network was, in part, recruited from preexisting network components that were present in the MRCA of angiosperms and modified to regulate gynoecium development.

The Evolutionary Aspects of Aquaporin Family

Aquaporins (AQPs ) are a family of transmembrane proteins present in almost all species including virus. They are grossly divided into three subfamilies based on the sequence around a highly conserved pore-forming NPA motif: (1) classical water -selective AQP (CAQP), (2) glycerol -permeable aquaglyceroporin (AQGP) and (3) AQP super-gene channel, superaquaporin (SAQP). AQP is composed of two tandem repeats of conserved three transmembrane domains and a NPA motif. AQP ancestors probably started in prokaryotes by the duplication of half AQP genes to be diversified into CAQPs or AQGPs by evolving a subfamily-specific carboxyl-terminal NPA motif. Both AQP subfamilies may have been carried over to unicellular eukaryotic ancestors, protists and further to multicellular organisms. Although fungus lineage has kept both AQP subfamilies, the plant lineage has lost AQGP after algal ancestors with extensive diversifications of CAQPs into PIP, TIP, SIP, XIP, HIP and LIP with a possible horizontal transfer of NIP from bacteria. Interestingly, the animal lineage has obtained new SAQP subfamily with highly deviated NPA motifs, especially at the amino-terminal halves in both prostomial and deuterostomial animals. The prostomial lineage has lost AQGP after hymenoptera, while the deuterostomial lineage has kept all three subfamilies up to the vertebrate with diversified CAQPs (AQP0, 1, 2, 4, 5, 6, 8) and AQGPs (AQP3, 7, 9, 10) with limited SAQPs (AQP11, 12) in mammals. Whole-genome duplications, local gene duplications and horizontal gene transfers may have produced the AQP diversity with adaptive selections and functional alternations in response to environment changes. With the above evolutionary perspective in mind, the function of each AQP could be speculated by comparison among species to get new insights into physiological roles of AQPs . This evolutionary guidance in AQP research will lead to deeper understandings of water and solute homeostasis.

Evolution of the Rax family of developmental transcription factors in vertebrates

Rax proteins comprise a small family of paired-type, homeodomain-containing transcription factors with essential functions in eye and forebrain development. While invertebrates possess only one Rax gene, vertebrates can have several Rax paralogue genes, but the evolutionary history of the members of the family has not been studied in detail. Here, we present a thorough analysis of the evolutionary relationships between vertebrate Rax genes and proteins available in diverse genomic databases. Phylogenetic and synteny analyses indicate that Rax genes went through a duplication in an ancestor of all jawed vertebrates (Gnathostomata), giving rise to the ancestral vertebrate Rax1 and Rax2 genes. This duplication event is likely related to the proposed polyploidisations that occurred during early vertebrate evolution. Subsequent genome-wide duplications in the lineage of ray-finned fish (Actinopterygii) originated new Rax2 paralogues in the genomes of teleosts. In the lobe-finned fish lineage (Sarcopterygii), the N-terminal octapeptide domain of Rax2 was lost in a common ancestor of tetrapods, giving rise to a shorter version of Rax2 in this lineage. Within placental mammals, the Rax2 gene was lost altogether in an ancestor of rodents and lagomorphs (Glires). Finally, we discuss the scientific literature in the light of Rax gene evolution and propose new avenues of research on the function of this important family of transcriptional regulators.

Corepressor diversification by alternative mRNA splicing is species specific

BACKGROUND

SMRT and NCoR are corepressor paralogs that help mediate transcriptional repression by a variety of transcription factors, including the nuclear hormone receptors. The functions of both corepressors are extensively diversified in mice by alternative mRNA splicing, generating a series of protein variants that differ in different tissues and that exert different, even diametrically opposite, biochemical and biological effects from one another.

RESULTS

We report here that the alternative splicing previously reported for SMRT appears to be a relatively recent evolutionary phenomenon, with only one of these previously identified sites utilized in a teleost fish and a limited additional number of the additional known sites utilized in a bird, reptile, and marsupial. In contrast, extensive SMRT alternative splicing at these sites was detected among the placental mammals. The alternative splicing of NCoR previously identified in mice (and shown to regulate lipid and carbohydrate metabolism) is likely to have arisen separately and after that of SMRT, and includes an example of convergent evolution.

CONCLUSIONS

We propose that the functions of both SMRT and NCoR have been diversified by alternative splicing during evolution to allow customization for different purposes in different tissues and different species.

Evolution history of duplicated smad3 genes in teleost: insights from Japanese flounder, Paralichthys olivaceus

Following the two rounds of whole-genome duplication (WGD) during deuterosome evolution, a third genome duplication occurred in the ray-fined fish lineage and is considered to be responsible for the teleost-specific lineage diversification and regulation mechanisms. As a receptor-regulated SMAD (R-SMAD), the function of SMAD3 was widely studied in mammals. However, limited information of its role or putative paralogs is available in ray-finned fishes. In this study, two SMAD3 paralogs were first identified in the transcriptome and genome of Japanese flounder (Paralichthys olivaceus). We also explored SMAD3 duplication in other selected species. Following identification, genomic structure, phylogenetic reconstruction, and synteny analyses performed by MrBayes and online bioinformatic tools confirmed that smad3a/3b most likely originated from the teleost-specific WGD. Additionally, selection pressure analysis and expression pattern of the two genes performed by PAML and quantitative real-time PCR (qRT-PCR) revealed evidence of subfunctionalization of the two SMAD3 paralogs in teleost. Our results indicate that two SMAD3 genes originate from teleost-specific WGD, remain transcriptionally active, and may have likely undergone subfunctionalization. This study provides novel insights to the evolution fates of smad3a/3b and draws attentions to future function analysis of SMAD3 gene family.

Phylogenetic-Derived Insights into the Evolution of Sialylation in Eukaryotes: Comprehensive Analysis of Vertebrate β-Galactoside α2,3/6-Sialyltransferases (ST3Gal and ST6Gal)

Cell surface of eukaryotic cells is covered with a wide variety of sialylated molecules involved in diverse biological processes and taking part in cell–cell interactions. Although the physiological relevance of these sialylated glycoconjugates in vertebrates begins to be deciphered, the origin and evolution of the genetic machinery implicated in their biosynthetic pathway are poorly understood. Among the variety of actors involved in the sialylation machinery, sialyltransferases are key enzymes for the biosynthesis of sialylated molecules. This review focus on β-galactoside α2,3/6-sialyltransferases belonging to the ST3Gal and ST6Gal families. We propose here an outline of the evolutionary history of these two major ST families. Comparative genomics, molecular phylogeny and structural bioinformatics provided insights into the functional innovations in sialic acid metabolism and enabled to explore how ST-gene function evolved in vertebrates.

Evolutionary origin and functional divergence of totipotent cell homeobox genes in eutherian mammals

BACKGROUND

A central goal of evolutionary biology is to link genomic change to phenotypic evolution. The origin of new transcription factors is a special case of genomic evolution since it brings opportunities for novel regulatory interactions and potentially the emergence of new biological properties.

RESULTS

We demonstrate that a group of four homeobox gene families (Argfx, Leutx, Dprx, Tprx), plus a gene newly described here (Pargfx), arose by tandem gene duplication from the retinal-expressed Crx gene, followed by asymmetric sequence evolution. We show these genes arose as part of repeated gene gain and loss events on a dynamic chromosomal region in the stem lineage of placental mammals, on the forerunner of human chromosome 19. The human orthologues of these genes are expressed specifically in early embryo totipotent cells, peaking from 8-cell to morula, prior to cell fate restrictions; cow orthologues have similar expression. To examine biological roles, we used ectopic gene expression in cultured human cells followed by high-throughput RNA-seq and uncovered extensive transcriptional remodelling driven by three of the genes. Comparison to transcriptional profiles of early human embryos suggest roles in activating and repressing a set of developmentally-important genes that spike at 8-cell to morula, rather than a general role in genome activation.

CONCLUSIONS

We conclude that a dynamic chromosome region spawned a set of evolutionarily new homeobox genes, the ETCHbox genes, specifically in eutherian mammals. After these genes diverged from the parental Crx gene, we argue they were recruited for roles in the preimplantation embryo including activation of genes at the 8-cell stage and repression after morula. We propose these new homeobox gene roles permitted fine-tuning of cell fate decisions necessary for specification and function of embryonic and extra-embryonic tissues utilised in mammalian development and pregnancy.

Evolution by gene loss

The recent increase in genomic data is revealing an unexpected perspective of gene loss as a pervasive source of genetic variation that can cause adaptive phenotypic diversity. This novel perspective of gene loss is raising new fundamental questions. How relevant has gene loss been in the divergence of phyla? How do genes change from being essential to dispensable and finally to being lost? Is gene loss mostly neutral, or can it be an effective way of adaptation? These questions are addressed, and insights are discussed from genomic studies of gene loss in populations and their relevance in evolutionary biology and biomedicine.