Reprimo tissue-specific expression pattern is conserved between zebrafish and human

Reprimo (RPRM), a member of the RPRM gene family, is a tumor-suppressor gene involved in the regulation of the p53-mediated cell cycle arrest at G2/M. RPRM has been associated with malignant tumor progression and proposed as a potential biomarker for early cancer detection. However, the expression and role of RPRM, as well as its family, are poorly understood and their physiology is as yet unstudied. In this scenario, a model system like the zebrafish could serve to dissect the role of the RPRM family members in vivo. Phylogenetic analysis reveals that RPRM and RPRML have been differentially retained by most species throughout vertebrate evolution, yet RPRM3 has been retained only in a small group of distantly related species, including zebrafish. Herein, we characterized the spatiotemporal expression of RPRM (present in zebrafish as an infraclass duplication rprma/rprmb), RPRML and RPRM3 in the zebrafish. By whole-mount in situ hybridization (WISH) and fluorescent in situ hybridization (FISH), we demonstrate that rprm (rprma/rprmb) and rprml show a similar spatiotemporal expression profile during zebrafish development. At early developmental stages rprmb is expressed in somites. After one day post-fertilization, rprm (rprma/rprmb) and rprml are expressed in the notochord, brain, blood vessels and digestive tube. On the other hand, rprm3 shows the most unique expression profile, being expressed only in the central nervous system (CNS). We assessed the expression patterns of RPRM gene transcripts in adult zebrafish and human RPRM protein product in tissue samples by RT-qPCR and immunohistochemistry (IHC) staining, respectively. Strikingly, tissue-specific expression patterns of the RPRM transcripts and protein are conserved between zebrafish and humans. We propose the zebrafish as a powerful tool to elucidate the both physiological and pathological roles of the RPRM gene family.

Evolution of gremlin 2 in cetartiodactyl mammals: gene loss coincides with lack of upper jaw incisors in ruminants

Understanding the processes that give rise to genomic variability in extant species is an active area of research within evolutionary biology. With the availability of whole genome sequences, it is possible to quantify different forms of variability such as variation in gene copy number, which has been described as an important source of genetic variability and in consequence of phenotypic variability. Most of the research on this topic has been focused on understanding the biological significance of gene duplication, and less attention has been given to the evolutionary role of gene loss. Gremlin 2 is a member of the DAN gene family and plays a significant role in tooth development by blocking the ligand-signaling pathway of BMP2 and BMP4. The goal of this study was to investigate the evolutionary history of gremlin 2 in cetartiodactyl mammals, a group that possesses highly divergent teeth morphology. Results from our analyses indicate that gremlin 2 has experienced a mixture of gene loss, gene duplication, and rate acceleration. Although the last common ancestor of cetartiodactyls possessed a single gene copy, pigs and camels are the only cetartiodactyl groups that have retained gremlin 2. According to the phyletic distribution of this gene and synteny analyses, we propose that gremlin 2 was lost in the common ancestor of ruminants and cetaceans between 56.3 and 63.5 million years ago as a product of a chromosomal rearrangement. Our analyses also indicate that the rate of evolution of gremlin 2 has been accelerated in the two groups that have retained this gene. Additionally, the lack of this gene could explain the high diversity of teeth among cetartiodactyl mammals; specifically, the presence of this gene could act as a biological constraint. Thus, our results support the notions that gene loss is a way to increase phenotypic diversity and that gremlin 2 is a dispensable gene, at least in cetartiodactyl mammals.

Evolution of the β-adrenoreceptors in vertebrates

The study of the evolutionary history of genes related to human disease lies at the interface of evolution and medicine. These studies provide the evolutionary context on which medical researchers should work, and are also useful in providing information to suggest further genetic experiments, especially in model species where genetic manipulations can be made. Here we studied the evolution of the β-adrenoreceptor gene family in vertebrates with the aim of adding an evolutionary framework to the already abundant physiological information. Our results show that in addition to the three already described vertebrate β-adrenoreceptor genes there is an additional group containing cyclostome sequences. We suggest that β-adrenoreceptors diversified as a product of the two whole genome duplications that occurred in the ancestor of vertebrates. Gene expression patterns are in general consistent across species, suggesting that expression dynamics were established early in the evolutionary history of vertebrates, and have been maintained since then. Finally, amino acid polymorphisms that are associated to pathological conditions in humans appear to be common in non-human mammals, suggesting that the phenotypic effects of these mutations depend on epistatic interaction with other positions. The evolutionary analysis of the β-adrenoreceptors delivers new insights about the diversity of these receptors in vertebrates, the evolution of the expression patterns and a comparative perspective regarding the polymorphisms that in humans are linked to pathological conditions.

Evolutionary history of the reprimo tumor suppressor gene family in vertebrates with a description of a new reprimo gene lineage

Genes related to human diseases should be natural targets for evolutionary studies, since they could provide clues regarding the genetic bases of pathologies and potential treatments. Here we studied the evolution of the reprimo gene family, a group of tumor-suppressor genes that are implicated in p53-mediated cell cycle arrest. These genes, especially the reprimo duplicate located on human chromosome 2, have been associated with epigenetic modifications correlated with transcriptional silencing and cancer progression. We demonstrate the presence of a third reprimo lineage that, together with the reprimo and reprimo-like genes, appears to have been differentially retained during the evolutionary history of vertebrates. We present evidence that these reprimo lineages originated early in vertebrate evolution and expanded as a result of the two rounds of whole genome duplications that occurred in the last common ancestor of vertebrates. The reprimo gene has been lost in birds, and the third reprimo gene lineage has been retained in only a few distantly related species, such as coelacanth and gar. Expression analyses revealed that the reprimo paralogs are mainly expressed in the nervous system. Different vertebrate lineages have retained different reprimo paralogs, and even in species that have retained multiple copies, only one of them is heavily expressed.

Lineage-Specific Expansion of the Chalcone Synthase Gene Family in Rosids

Rosids are a monophyletic group that includes approximately 70,000 species in 140 families, and they are found in a variety of habitats and life forms. Many important crops such as fruit trees and legumes are rosids. The evolutionary success of this group may have been influenced by their ability to produce flavonoids, secondary metabolites that are synthetized through a branch of the phenylpropanoid pathway where chalcone synthase is a key enzyme. In this work, we studied the evolution of the chalcone synthase gene family in 12 species belonging to the rosid clade. Our results show that the last common ancestor of the rosid clade possessed six chalcone synthase gene lineages that were differentially retained during the evolutionary history of the group. In fact, of the six gene lineages that were present in the last common ancestor, 7 species retained 2 of them, whereas the other 5 only retained one gene lineage. We also show that one of the gene lineages was disproportionately expanded in species that belonged to the order Fabales (soybean, barrel medic and Lotus japonicas). Based on the available literature, we suggest that this gene lineage possesses stress-related biological functions (e.g., response to UV light, pathogen defense). We propose that the observed expansion of this clade was a result of a selective pressure to increase the amount of enzymes involved in the production of phenylpropanoid pathway-derived secondary metabolites, which is consistent with the hypothesis that suggested that lineage-specific expansions fuel plant adaptation.

Gene turnover in the avian globin gene families and evolutionary changes in hemoglobin isoform expression

The apparent stasis in the evolution of avian chromosomes suggests that birds may have experienced relatively low rates of gene gain and loss in multigene families. To investigate this possibility and to explore the phenotypic consequences of variation in gene copy number, we examined evolutionary changes in the families of genes that encode the α- and β-type subunits of hemoglobin (Hb), the tetrameric α2β2 protein responsible for blood-O2 transport. A comparative genomic analysis of 52 bird species revealed that the size and membership composition of the α- and β-globin gene families have remained remarkably constant during approximately 100 My of avian evolution. Most interspecific variation in gene content is attributable to multiple independent inactivations of the α(D)-globin gene, which encodes the α-chain subunit of a functionally distinct Hb isoform (HbD) that is expressed in both embryonic and definitive erythrocytes. Due to consistent differences in O2-binding properties between HbD and the major adult-expressed Hb isoform, HbA (which incorporates products of the α(A)-globin gene), recurrent losses of α(D)-globin contribute to among-species variation in blood-O2 affinity. Analysis of HbA/HbD expression levels in the red blood cells of 122 bird species revealed high variability among lineages and strong phylogenetic signal. In comparison with the homologous gene clusters in mammals, the low retention rate for lineage-specific gene duplicates in the avian globin gene clusters suggests that the developmental regulation of Hb synthesis in birds may be more highly conserved, with orthologous genes having similar stage-specific expression profiles and similar functional properties in disparate taxa.

Ancient Duplications and Expression Divergence in the Globin Gene Superfamily of Vertebrates: Insights from the Elephant Shark Genome and Transcriptome

Comparative analyses of vertebrate genomes continue to uncover a surprising diversity of genes in the globin gene superfamily, some of which have very restricted phyletic distributions despite their antiquity. Genomic analysis of the globin gene repertoire of cartilaginous fish (Chondrichthyes) should be especially informative about the duplicative origins and ancestral functions of vertebrate globins, as divergence between Chondrichthyes and bony vertebrates represents the most basal split within the jawed vertebrates. Here, we report a comparative genomic analysis of the vertebrate globin gene family that includes the complete globin gene repertoire of the elephant shark (Callorhinchus milii). Using genomic sequence data from representatives of all major vertebrate classes, integrated analyses of conserved synteny and phylogenetic relationships revealed that the last common ancestor of vertebrates possessed a repertoire of at least seven globin genes: single copies of androglobin and neuroglobin, four paralogous copies of globin X, and the single-copy progenitor of the entire set of vertebrate-specific globins. Combined with expression data, the genomic inventory of elephant shark globins yielded four especially surprising findings: 1) there is no trace of the neuroglobin gene (a highly conserved gene that is present in all other jawed vertebrates that have been examined to date), 2) myoglobin is highly expressed in heart, but not in skeletal muscle (reflecting a possible ancestral condition in vertebrates with single-circuit circulatory systems), 3) elephant shark possesses two highly divergent globin X paralogs, one of which is preferentially expressed in gonads, and 4) elephant shark possesses two structurally distinct α-globin paralogs, one of which is preferentially expressed in the brain. Expression profiles of elephant shark globin genes reveal distinct specializations of function relative to orthologs in bony vertebrates and suggest hypotheses about ancestral functions of vertebrate globins.

Three crocodilian genomes reveal ancestral patterns of evolution among archosaurs

To provide context for the diversification of archosaurs--the group that includes crocodilians, dinosaurs, and birds--we generated draft genomes of three crocodilians: Alligator mississippiensis (the American alligator), Crocodylus porosus (the saltwater crocodile), and Gavialis gangeticus (the Indian gharial). We observed an exceptionally slow rate of genome evolution within crocodilians at all levels, including nucleotide substitutions, indels, transposable element content and movement, gene family evolution, and chromosomal synteny. When placed within the context of related taxa including birds and turtles, this suggests that the common ancestor of all of these taxa also exhibited slow genome evolution and that the comparatively rapid evolution is derived in birds. The data also provided the opportunity to analyze heterozygosity in crocodilians, which indicates a likely reduction in population size for all three taxa through the Pleistocene. Finally, these data combined with newly published bird genomes allowed us to reconstruct the partial genome of the common ancestor of archosaurs, thereby providing a tool to investigate the genetic starting material of crocodilians, birds, and dinosaurs.

Comparative genomics reveals insights into avian genome evolution and adaptation

Birds are the most species-rich class of tetrapod vertebrates and have wide relevance across many research fields. We explored bird macroevolution using full genomes from 48 avian species representing all major extant clades. The avian genome is principally characterized by its constrained size, which predominantly arose because of lineage-specific erosion of repetitive elements, large segmental deletions, and gene loss. Avian genomes furthermore show a remarkably high degree of evolutionary stasis at the levels of nucleotide sequence, gene synteny, and chromosomal structure. Despite this pattern of conservation, we detected many non-neutral evolutionary changes in protein-coding genes and noncoding regions. These analyses reveal that pan-avian genomic diversity covaries with adaptations to different lifestyles and convergent evolution of traits.

Evolution of the relaxin/insulin-like gene family in anthropoid primates

The relaxin/insulin-like gene family includes signaling molecules that perform a variety of physiological roles mostly related to reproduction and neuroendocrine regulation. Several previous studies have focused on the evolutionary history of relaxin genes in anthropoid primates, with particular attention on resolving the duplication history of RLN1 and RLN2 genes, which are found as duplicates only in apes. These studies have revealed that the RLN1 and RLN2 paralogs in apes have a more complex history than their phyletic distribution would suggest. In this regard, alternative scenarios have been proposed to explain the timing of duplication, and the history of gene gain and loss along the organismal tree. In this article, we revisit the question and specifically reconstruct phylogenies based on coding and noncoding sequence in anthropoid primates to readdress the timing of the duplication event giving rise to RLN1 and RLN2 in apes. Results from our phylogenetic analyses based on noncoding sequence revealed that the duplication event that gave rise to the RLN1 and RLN2 occurred in the last common ancestor of catarrhine primates, between ∼44.2 and 29.6 Ma, and not in the last common ancestor of apes or anthropoids, as previously suggested. Comparative analyses based on coding and noncoding sequence suggests an event of convergent evolution at the sequence level between co-ortholog genes, the single-copy RLN gene found in New World monkeys and the RLN1 gene of apes, where changes in a fraction of the convergent sites appear to be driven by positive selection.

Increased rate of hair keratin gene loss in the cetacean lineage

BACKGROUND

Hair represents an evolutionary innovation that appeared early on mammalian evolutionary history, and presumably contributed significantly to the rapid radiation of the group. An interesting event in hair evolution has been its secondary loss in some mammalian groups, such as cetaceans, whose hairless phenotype appears to be an adaptive response to better meet the environmental conditions. To determine whether different repertoire of keratin genes among mammals can potentially explain the phenotypic hair features of different lineages, we characterized the type I and II clusters of alpha keratins from eight mammalian species, including the hairless dolphin and minke whale representing the order Cetacea.

RESULTS

We combined the available genomic information with phylogenetic analysis to conduct a comprehensive analysis of the evolutionary patterns of keratin gene clusters. We found that both type I and II gene clusters are fairly conserved among the terrestrial mammals included in this study, with lineage specific gene duplication and gene loss. Nevertheless, there is also evidence for an increased rate of pseudogenization in the cetacean lineage when compared to their terrestrial relatives, especially among the hair type keratins.

CONCLUSIONS

Here we present a comprehensive characterization of alpha-keratin genes among mammals and elucidate the mechanisms involved in the evolution of this gene family. We identified lineage-specific gene duplications and gene loss among the Laurasiatherian and Euarchontoglires species included in the study. Interestingly, cetaceans present an increased loss of hair-type keratin genes when compared to other terrestrial mammals. As suggested by the 'less-is-more' hypothesis, we do not rule out the possibility that the gene loss of hair-type keratin genes in these species might be associated to the hairless phenotype and could have been adaptive in response to new selective pressures imposed by the colonization of a new habitat. Our study provides support for the idea that pseudogenes are not simply 'genomic fossils' but instead have adaptive roles during the evolutionary process.

Genomic organization and differential signature of positive selection in the alpha and beta globin gene clusters in two cetacean species

The hemoglobin of jawed vertebrates is a heterotetramer protein that contains two α- and two β-chains, which are encoded by members of α- and β-globin gene families. Given the hemoglobin role in mediating an adaptive response to chronic hypoxia, it is likely that this molecule may have experienced a selective pressure during the evolution of cetaceans, which have to deal with hypoxia tolerance during prolonged diving. This selective pressure could have generated a complex history of gene turnover in these clusters and/or changes in protein structure themselves. Accordingly, we aimed to characterize the genomic organization of α- and β-globin gene clusters in two cetacean species and to detect a possible role of positive selection on them using a phylogenetic framework. Maximum likelihood and Bayesian phylogeny reconstructions revealed that both cetacean species had retained a similar complement of putatively functional genes. For the α-globin gene cluster, the killer whale presents a complement of genes composed of HBZ, HBK, and two functional copies of HBA and HBQ genes, whereas the dolphin possesses HBZ, HBK, HBA and HBQ genes, and one HBA pseudogene. For the β-globin gene cluster, both species retained a complement of four genes, two early expressed genes—HBE and HBH—and two adult expressed genes—HBD and HBB. Our natural selection analysis detected two positively selected sites in the HBB gene (56 and 62) and four in HBA (15, 21, 49, 120). Interestingly, only the genes that are expressed during the adulthood showed the signature of positive selection.

Characterization of the kidney transcriptome of the South American olive mouse Abrothrix olivacea

BACKGROUND

The olive mouse Abrothrix olivacea is a cricetid rodent of the subfamily Sigmodontinae that inhabits a wide range of contrasting environments in southern South America, from aridlands to temperate rainforests. Along its distribution, it presents different geographic forms that make the olive mouse a good focal case for the study of geographical variation in response to environmental variation. We chose to characterize the kidney transcriptome because this organ has been shown to be associated with multiple physiological processes, including water reabsorption.

RESULTS

Transcriptomes of thirteen kidneys from individuals from Argentina and Chile were sequenced using Illumina technology in order to obtain a kidney reference transcriptome. After combining the reads produced for each sample, we explored three assembly strategies to obtain the best reconstruction of transcripts, TrinityNorm and DigiNorm, which include its own normalization algorithms for redundant reads removal, and Multireads, which simply consist on the assembly of the joined reads. We found that Multireads strategy produces a less fragmented assembly than normalization algorithms but recovers fewer number of genes. In general, about 15000 genes were annotated, of which almost half had at least one coding sequence reconstructed at 99% of its length. We also built a list of highly expressed genes, of which several are involved in water conservation under laboratory conditions using mouse models.

CONCLUSION

Based on our assembly results, Trinity's in silico normalization is the best algorithm in terms of cost-benefit returns; however, our results also indicate that normalization should be avoided if complete or nearly complete coding sequences of genes are desired. Given that this work is the first to characterize the transcriptome of any member of Sigmodontinae, a subfamily of cricetid rodents with about 400 living species, it will provide valuable resources for future ecological and evolutionary genomic analyses.

The complete mitochondrial genome of the land snail Cornu aspersum (Helicidae: Mollusca): intra-specific divergence of protein-coding genes and phylogenetic considerations within Euthyneura

The complete sequences of three mitochondrial genomes from the land snail Cornu aspersum were determined. The mitogenome has a length of 14050 bp, and it encodes 13 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes. It also includes nine small intergene spacers, and a large AT-rich intergenic spacer. The intra-specific divergence analysis revealed that COX1 has the lower genetic differentiation, while the most divergent genes were NADH1, NADH3 and NADH4. With the exception of Euhadra herklotsi, the structural comparisons showed the same gene order within the family Helicidae, and nearly identical gene organization to that found in order Pulmonata. Phylogenetic reconstruction recovered Basommatophora as polyphyletic group, whereas Eupulmonata and Pulmonata as paraphyletic groups. Bayesian and Maximum Likelihood analyses showed that C. aspersum is a close relative of Cepaea nemoralis, and with the other Helicidae species form a sister group of Albinaria caerulea, supporting the monophyly of the Stylommatophora clade.

How to Make a Dolphin: Molecular Signature of Positive Selection in Cetacean Genome

Cetaceans are unique in being the only mammals completely adapted to an aquatic environment. This adaptation has required complex changes and sometimes a complete restructuring of physiology, behavior and morphology. Identifying genes that have been subjected to selection pressure during cetacean evolution would greatly enhance our knowledge of the ways in which genetic variation in this mammalian order has been shaped by natural selection. Here, we performed a genome-wide scan for positive selection in the dolphin lineage. We employed models of codon substitution that account for variation of selective pressure over branches on the tree and across sites in a sequence. We analyzed 7,859 nuclear-coding ortholog genes and using a series of likelihood ratio tests (LRTs), we identified 376 genes (4.8%) with molecular signatures of positive selection in the dolphin lineage. We used the cow as the sister group and compared estimates of selection in the cetacean genome to this using the same methods. This allowed us to define which genes have been exclusively under positive selection in the dolphin lineage. The enrichment analysis found that the identified positively selected genes are significantly over-represented for three exclusive functional categories only in the dolphin lineage: segment specification, mesoderm development and system development. Of particular interest for cetacean adaptation to an aquatic life are the following GeneOntology targets under positive selection: genes related to kidney, heart, lung, eye, ear and nervous system development.

Whole-genome duplication and the functional diversification of teleost fish hemoglobins

Subsequent to the two rounds of whole-genome duplication that occurred in the common ancestor of vertebrates, a third genome duplication occurred in the stem lineage of teleost fishes. This teleost-specific genome duplication (TGD) is thought to have provided genetic raw materials for the physiological, morphological, and behavioral diversification of this highly speciose group. The extreme physiological versatility of teleost fish is manifest in their diversity of blood–gas transport traits, which reflects the myriad solutions that have evolved to maintain tissue O₂ delivery in the face of changing metabolic demands and environmental O₂ availability during different ontogenetic stages. During the course of development, regulatory changes in blood–O₂ transport are mediated by the expression of multiple, functionally distinct hemoglobin (Hb) isoforms that meet the particular O₂-transport challenges encountered by the developing embryo or fetus (in viviparous or oviparous species) and in free-swimming larvae and adults. The main objective of the present study was to assess the relative contributions of whole-genome duplication, large-scale segmental duplication, and small-scale gene duplication in producing the extraordinary functional diversity of teleost Hbs. To accomplish this, we integrated phylogenetic reconstructions with analyses of conserved synteny to characterize the genomic organization and evolutionary history of the globin gene clusters of teleosts. These results were then integrated with available experimental data on functional properties and developmental patterns of stage-specific gene expression. Our results indicate that multiple α- and β-globin genes were present in the common ancestor of gars (order Lepisoteiformes) and teleosts. The comparative genomic analysis revealed that teleosts possess a dual set of TGD-derived globin gene clusters, each of which has undergone lineage-specific changes in gene content via repeated duplication and deletion events. Phylogenetic reconstructions revealed that paralogous genes convergently evolved similar functional properties in different teleost lineages. Consistent with other recent studies of globin gene family evolution in vertebrates, our results revealed evidence for repeated evolutionary transitions in the developmental regulation of Hb synthesis.

Gene duplication, genome duplication, and the functional diversification of vertebrate globins

The functional diversification of the vertebrate globin gene superfamily provides an especially vivid illustration of the role of gene duplication and whole-genome duplication in promoting evolutionary innovation. For example, key globin proteins that evolved specialized functions in various aspects of oxidative metabolism and oxygen signaling pathways (hemoglobin [Hb], myoglobin [Mb], and cytoglobin [Cygb]) trace their origins to two whole-genome duplication events in the stem lineage of vertebrates. The retention of the proto-Hb and Mb genes in the ancestor of jawed vertebrates permitted a physiological division of labor between the oxygen-carrier function of Hb and the oxygen-storage function of Mb. In the Hb gene lineage, a subsequent tandem gene duplication gave rise to the proto α- and β-globin genes, which permitted the formation of multimeric Hbs composed of unlike subunits (α(2)β(2)). The evolution of this heteromeric quaternary structure was central to the emergence of Hb as a specialized oxygen-transport protein because it provided a mechanism for cooperative oxygen-binding and allosteric regulatory control. Subsequent rounds of duplication and divergence have produced diverse repertoires of α- and β-like globin genes that are ontogenetically regulated such that functionally distinct Hb isoforms are expressed during different stages of prenatal development and postnatal life. In the ancestor of jawless fishes, the proto Mb and Hb genes appear to have been secondarily lost, and the Cygb homolog evolved a specialized respiratory function in blood-oxygen transport. Phylogenetic and comparative genomic analyses of the vertebrate globin gene superfamily have revealed numerous instances in which paralogous globins have convergently evolved similar expression patterns and/or similar functional specializations in different organismal lineages.

Evolution of the globin gene family in deuterostomes: lineage-specific patterns of diversification and attrition

In the Metazoa, globin proteins display an underlying unity in tertiary structure that belies an extraordinary diversity in primary structures, biochemical properties, and physiological functions. Phylogenetic reconstructions can reveal which of these functions represent novel, lineage-specific innovations, and which represent ancestral functions that are shared with homologous globin proteins in other eukaryotes and even prokaryotes. To date, our understanding of globin diversity in deuterostomes has been hindered by a dearth of genomic sequence data from the Ambulacraria (echinoderms + hemichordates), the sister group of chordates, and the phylum Xenacoelomorpha, which includes xenoturbellids, acoelomorphs, and nemertodermatids. Here, we report the results of a phylogenetic and comparative genomic analysis of the globin gene repertoire of deuterostomes. We first characterized the globin genes of the acorn worm, Saccoglossus kowalevskii, a representative of the phylum Hemichordata. We then integrated genomic sequence data from the acorn worm into a comprehensive analysis of conserved synteny and phylogenetic relationships among globin genes from representatives of the eight lineages that comprise the superphylum Deuterostomia. The primary aims were 1) to unravel the evolutionary history of the globin gene superfamily in deuterostomes and 2) to use the estimated phylogeny to gain insights into the functional evolution of deuterostome globins. Results of our analyses indicate that the deuterostome common ancestor possessed a repertoire of at least four distinct globin paralogs and that different subsets of these ancestral genes have been retained in each of the descendant organismal lineages. In each major deuterostome group, a different subset of ancestral precursor genes underwent lineage-specific expansions of functional diversity through repeated rounds of gene duplication and divergence. By integrating results of the phylogenetic analysis with available functional data, we discovered that circulating oxygen-transport hemoglobins evolved independently in several deuterostome lineages and that intracellular nerve globins evolved independently in chordates and acoelomorph worms.

Gene turnover and differential retention in the relaxin/insulin-like gene family in primates

The relaxin/insulin-like gene family is related to the insulin gene family, and includes two separate types of peptides: relaxins (RLNs) and insulin-like peptides (INSLs) that perform a variety of physiological roles including testicular descent, growth and differentiation of the mammary glands, trophoblast development, and cell differentiation. In vertebrates, these genes are found on three separate genomic loci, and in mammals, variation in the number and nature of genes in this family is mostly restricted to the Relaxin Family Locus B. For example, this locus contains a single copy of RLN in platypus and opossum, whereas it contains copies of the INSL6, INSL4, RLN2 and RLN1 genes in human and chimp. The main objective of this research is to characterize changes in the size and membership composition of the RLN/INSL gene family in primates, reconstruct the history of the RLN/INSL genes of primates, and test competing evolutionary scenarios regarding the origin of INSL4 and of the duplicated copies of the RLN gene of apes. Our results show that the relaxin/INSL-like gene family of primates has had a more dynamic evolutionary history than previously thought, including several examples of gene duplications and losses which are consistent with the predictions of the birth-and-death model of gene family evolution. In particular, we found that the differential retention of relatively old paralogs played a key role in shaping the gene complement of this family in primates. Two examples of this phenomenon are the origin of the INSL4 gene of catarrhines (the group that includes Old World monkeys and apes), and of the duplicate RLN1 and RLN2 paralogs of apes. In the case of INSL4, comparative genomics and phylogenetic analyses indicate that the origin of this gene, which was thought to represent a catarrhine-specific evolutionary innovation, is as old as the split between carnivores and primates, which took place approximately 97 million years ago. In addition, in the case of the RLN1 and RLN2 genes of apes our phylogenetic trees and topology tests indicate that the duplication that gave rise to these two genes maps to the last common ancestor of anthropoid primates. All these genomic changes in gene complement, which are particularly prevalent among anthropoid primates, might be linked to the many physiological and anatomical changes found in this group. Given the various roles of members of the RLN/INSL-like gene family in reproductive biology, it might be that changes in this gene family are associated to changes in reproductive traits.

Silencing, positive selection and parallel evolution: busy history of primate cytochromes C

Cytochrome c (cyt c) participates in two crucial cellular processes, energy production and apoptosis, and unsurprisingly is a highly conserved protein. However, previous studies have reported for the primate lineage (i) loss of the paralogous testis isoform, (ii) an acceleration and then a deceleration of the amino acid replacement rate of the cyt c somatic isoform, and (iii) atypical biochemical behavior of human cyt c. To gain insight into the cause of these major evolutionary events, we have retraced the history of cyt c loci among primates. For testis cyt c, all primate sequences examined carry the same nonsense mutation, which suggests that silencing occurred before the primates diversified. For somatic cyt c, maximum parsimony, maximum likelihood, and Bayesian phylogenetic analyses yielded the same tree topology. The evolutionary analyses show that a fast accumulation of non-synonymous mutations (suggesting positive selection) occurred specifically on the anthropoid lineage root and then continued in parallel on the early catarrhini and platyrrhini stems. Analysis of evolutionary changes using the 3D structure suggests they are focused on the respiratory chain rather than on apoptosis or other cyt c functions. In agreement with previous biochemical studies, our results suggest that silencing of the cyt c testis isoform could be linked with the decrease of primate reproduction rate. Finally, the evolution of cyt c in the two sister anthropoid groups leads us to propose that somatic cyt c evolution may be related both to COX evolution and to the convergent brain and body mass enlargement in these two anthropoid clades.

Whole-genome duplications spurred the functional diversification of the globin gene superfamily in vertebrates

It has been hypothesized that two successive rounds of whole-genome duplication (WGD) in the stem lineage of vertebrates provided genetic raw materials for the evolutionary innovation of many vertebrate-specific features. However, it has seldom been possible to trace such innovations to specific functional differences between paralogous gene products that derive from a WGD event. Here, we report genomic evidence for a direct link between WGD and key physiological innovations in the vertebrate oxygen transport system. Specifically, we demonstrate that key globin proteins that evolved specialized functions in different aspects of oxidative metabolism (hemoglobin, myoglobin, and cytoglobin) represent paralogous products of two WGD events in the vertebrate common ancestor. Analysis of conserved macrosynteny between the genomes of vertebrates and amphioxus (subphylum Cephalochordata) revealed that homologous chromosomal segments defined by myoglobin + globin-E, cytoglobin, and the α-globin gene cluster each descend from the same linkage group in the reconstructed proto-karyotype of the chordate common ancestor. The physiological division of labor between the oxygen transport function of hemoglobin and the oxygen storage function of myoglobin played a pivotal role in the evolution of aerobic energy metabolism, supporting the hypothesis that WGDs helped fuel key innovations in vertebrate evolution.