Epidemiología molecular de la colonización nasofaríngea neumocócica en niños de Sevilla, tras la implementación del programa de vacunación con VNC13 en Andalucía (España) / Molecular epidemiology of pneumococcal carriage in children from Seville, following implementation of the PCV13 immunization program in Andalusia, Spain

Introducción: El programa de vacunación universal con la vacuna antineumocócica conjugada 13-valente (VNC13) se implantó en Andalucía en diciembre de 2016. Métodos: Estudio transversal de colonización nasofaríngea por Streptococcus pneumoniae. Se seleccionó a 397 niños sanos en centros de atención primaria de Sevilla durante los periodos 1/4/2018-28/2/2020 y 1/11/2021-28/2/2022 (periodo VNC13). Se utilizó una colección histórica de un estudio de colonización desarrollado en niños sanos y con infección respiratoria superior entre el 1/01/2006 y el 30/06/2008 (periodo VNC7) para comparar las distribuciones de serotipos/genotipos y las tasas de resistencias antibióticas. Resultados: Un total de 76 (19%) niños estaban colonizados con S. pneumoniae en el periodo VNC13 y se dispuso de 154 aislamientos del periodo VNC7. La colonización por serotipos incluidos en VNC13 disminuyó significativamente entre los periodos VNC13 y VNC7 (11 vs. 38%; p=0,0001); los serotipos 19F (8%), 3 (1%) y 6B (1%) fueron los únicos serotipos vacunales circulantes. Los serotipos 15B/C y 11A fueron los serotipos no VNC13 más prevalentes durante el periodo VNC13 (14% y 11%, respectivamente); este último se incrementó de forma significativa entre periodos de tiempo (p=0,04). El serotipo 11A solo se asoció en el periodo VNC13 con variantes resistentes a la ampicilina del clon Spain9V-ST156 (ST6521 y genéticamente relacionado ST14698), no detectados en el periodo anterior. Conclusiones: Hubo una circulación muy residual de los serotipos vacunales durante el periodo VNC13, con excepción del serotipo19F. El serotipo 11A se incrementó de forma significativa entre los periodos VNC13 y VNC7 por expansión clonal del genotipo resistente a la ampicilina ST6521.(AU)

Background: The 13-valent pneumococcal conjugate vaccine (PCV13) universal vaccination program was introduced in December 2016 in Andalusia. Methods: A cross-sectional study was conducted on the molecular epidemiology of pneumococcal nasopharyngeal colonization. A total of 397 healthy children were recruited from primary healthcare centres in Seville for the periods 1/4/2018 to 28/2/2020 and 1/11/2021 to 28/2/2022 (PCV13 period). Data from a previous carriage study conducted among healthy and sick children from 1/01/2006 to 30/06/2008 (PCV7 period) were used for comparison of serotype/genotype distributions and antibiotic resistance rates. Results: Overall, 76 (19%) children were colonized with S. pneumoniae during the PCV13 period and there were information available from 154 isolates collected during the PCV7 period. Colonization with PCV13 serotypes declined significantly in the PCV13 period compared with historical controls (11 vs. 38%, P=0.0001), being serotypes 19F (8%), 3 (1%) and 6B (1%) the only circulating vaccine types. Serotypes 15B/C and 11A were the most frequently identified non-PCV13 serotypes during the PCV13 period (14% and 11%, respectively); the later one increased significantly between time periods (P=0.04). Serotype 11A was exclusively associated in the PCV13 period with ampicillin-resistant variants of the Spain9V-ST156 clone (ST6521 and genetically related ST14698), not detected in the preceding period. Conclusions: There was a residual circulation of vaccine types following PCV13 introduction, apart from serotype 19F. Serotype 11A increased between PCV13 and PCV7 periods due to emergence and clonal expansion of ampicillin-resistant genotype ST6521.(AU)

Molecular epidemiology of pneumococcal carriage in children from Seville, following implementation of the PCV13 immunization program in Andalusia, Spain.

INTRODUCTION: The 13-valent pneumococcal conjugate vaccine (PCV13) universal vaccination programme was introduced in December 2016 in Andalusia. METHODS: A cross-sectional study was conducted on the molecular epidemiology of pneumococcal nasopharyngeal colonization. A total of 397 healthy children were recruited from primary healthcare centres in Seville for the periods 1/4/2018 to 28/2/2020 and 1/11/2021 to 28/2/2022 (PCV13 period). Data from a previous carriage study conducted among healthy and sick children from 1/01/2006 to 30/06/2008 (PCV7 period), were used for comparison of serotype/genotype distributions and antibiotic resistance rates. RESULTS: Overall, 76 (19%) children were colonized with S. pneumoniae during the PCV13 period and there were information available from 154 isolates collected during the PCV7 period. Colonization with PCV13 serotypes declined significantly in the PCV13 period compared with historical controls (11% vs 38%, p = 0.0001), being serotypes 19F (8%), 3 (1%) and 6B (1%) the only circulating vaccine types. Serotypes 15B/C and 11A were the most frequently identified non-PCV13 serotypes during the PCV13 period (14% and 11%, respectively); the later one increased significantly between time periods (p = 0.04). Serotype 11A was exclusively associated in the PCV13 period with ampicillin-resistant variants of the Spain9V-ST156 clone (ST6521 and genetically related ST14698), not detected in the preceding period. CONCLUSIONS: There was a residual circulation of vaccine types following PCV13 introduction, apart from serotype 19F. Serotype 11A increased between PCV13 and PCV7 periods due to emergence and clonal expansion of ampicillin-resistant genotype ST6521.

"Long-term oncologic outcomes and risk factors for distant recurrence after pathologic complete response following neoadjuvant treatment for locally advanced rectal cancer. A nationwide, multicentre study".

BACKGROUND: Pathologic complete response (pCR) after multimodal treatment for locally advanced rectal cancer (LARC) is used as surrogate marker of success as it is assumed to correlate with improved oncologic outcome. However, long-term oncologic data are scarce. METHODS: This retrospective, multicentre study updated the oncologic follow-up of prospectively collected data from the Spanish Rectal Cancer Project database. pCR was described as no evidence of tumour cells in the specimen. Endpoints were distant metastases-free survival (DMFS) and overall survival (OS). Multivariate regression analyses were run to identify factors associated with survival. RESULTS: Overall, 32 different hospitals were involved, providing data on 815 patients with pCR. At a median follow-up of 73.4 (IQR 57.7-99.5) months, distant metastases occurred in 6.4% of patients. Abdominoperineal excision (APE) (HR 2.2, 95%CI 1.2-4.1, p = 0.008) and elevated CEA levels (HR = 1.9, 95% CI 1.0-3.7, p = 0.049) were independent risk factors for distant recurrence. Age (years) (HR 1.1; 95%-CI 1.05-41.09; p < 0.001) and ASA III-IV (HR = 2.0; 95%-CI 1.4-2.9; p < 0.001), were the only factors associated with OS. The estimated 12, 36 and 60-months DMFS rates were 96.9%, 91.3%, and 86.8%. The estimated 12, 36 and 60-months OS rates were 99.1%, 94.9% and 89.3%. CONCLUSIONS: The incidence of metachronous distant metastases is low after pCR, with high rates of both DMFS and OS. The oncologic prognosis in LARC patients that achieve pCR after neoadjuvant chemo-radiotherapy is excellent in the long term.

Linking pathogen-microbiome-host interactions to explain amphibian population dynamics.

Symbiotic interactions can determine the evolutionary trajectories of host species, influencing genetic variation through selection and changes in demography. In the context of strong selective pressures such as those imposed by infectious diseases, symbionts providing defences could contribute to increase host fitness upon pathogen emergence. Here, we generated genome-wide data of an amphibian species to find evidence of evolutionary pressures driven by two skin symbionts: a batrachochytrid fungal pathogen and an antifungal bacterium. Using demographic modelling, we found evidence of decreased effective population size, probably due to pathogen infections. Additionally, we investigated host genetic associations with infection status, antifungal bacterium abundance and overall microbiome diversity using structural equation models. We uncovered relatively lower nucleotide diversity in infected frogs and potential heterozygote advantage to recruit the candidate beneficial symbiont and fight infections. Our models indicate that environmental conditions have indirect effects on symbiont abundance through both host body traits and microbiome diversity. Likewise, we uncovered a potential offsetting effect among host heterozygosity-fitness correlations, plausibly pointing to different ecological and evolutionary processes among the three species due to dynamic interactions. Our findings revealed that evolutionary pressures not only arise from the pathogen but also from the candidate beneficial symbiont, and both interactions shape the genetics of the host. Our results advance knowledge about multipartite symbiotic relationships and provide a framework to model ecological and evolutionary dynamics in wild populations. Finally, our study approach can be applied to inform conservation actions such as bioaugmentation strategies for other imperilled amphibians affected by infectious diseases.

Molecular epidemiology of paediatric invasive pneumococcal disease in Andalusia, Spain.

This study aimed to assess the impact of the introduction of pneumococcal conjugate vaccine 13 (PCV13) on the molecular epidemiology of invasive pneumococcal disease (IPD) in children from Andalusia. A population-based prospective surveillance study was conducted on IPD in children aged <14 years from Andalusia (2018-2020). Pneumococcal invasive isolates collected between 2006 and 2009 in the two largest tertiary hospitals in Andalusia were used as pre-PCV13 controls for comparison of serotype/genotype distribution. Overall IPD incidence rate was 3.55 cases per 100 000 in 2018; increased non-significantly to 4.20 cases per 100 000 in 2019 and declined in 2020 to 1.69 cases per 100 000 (incidence rate ratio 2020 vs. 2019: 0.40, 95% confidence interval (CI) 0.20-0.89, P = 0.01). Proportion of IPD cases due to PCV13 serotypes in 2018-2020 was 28% (P = 0.0001 for comparison with 2006-2009). Serotypes 24F (15%) and 11A (8.3%) were the most frequently identified non-PCV13 serotypes (NVT) in 2018-2020. Penicillin- and/or ampicillin-resistant clones mostly belonged to clonal complex 156 (serotype 14-ST156 and ST2944 and serotype 11A-ST6521). The proportion of IPD cases caused by PCV13 serotypes declined significantly after the initiation of the PCV13 vaccination programme in 2016. Certain NVT, such as serotypes 24F and 11A, warrant future monitoring in IPD owing to invasive potential and/or antibiotic resistance rates.

Panzootic chytrid fungus exploits diverse amphibian host environments through plastic infection strategies.

While some pathogens are limited to single species, others can colonize many hosts, likely contributing to the emergence of novel disease outbreaks. Despite this biodiversity threat, traits associated with host niche expansions are not well understood in multihost pathogens. Here, we aimed to uncover functional machinery driving multihost invasion by focusing on Batrachochytrium dendrobatidis (Bd), a pathogen that infects the skin of hundreds of amphibians worldwide. We performed a meta-analysis of Bd gene expression using data from published infection experiments and newly generated profiles. We analysed Bd transcriptomic landscapes across the skin of 14 host species, reconstructed Bd isolates phylogenetic relationships, and inferred the origin and evolutionary history of differentially expressed genes under a phylogenetic framework comprising other 12 zoosporic fungi. Bd displayed plastic infection strategies when challenged by hosts with different disease susceptibility. Our analyses identified sets of differentially expressed genes under host environments with similar infection outcome. We stressed nutritional immunity and gene silencing as important processes required to overcome challenging skin environments in less susceptible hosts. Overall, Bd genes expressed during amphibian skin exploitation have arisen mainly via gene duplications with great family expansions, increasing the gene copy events previously described for this fungal species. Finally, we provide a comprehensive gene data set that can be used to further examine eco-evolutionary hypotheses for this host-pathogen system. Our study supports the idea that host environments exert contrasting selective pressures, such that gene expression plasticity could be one of the evolutionary keys leading to the success of multihost pathogens.

A survey of shared pathogens at the domestic-wild ruminants' interface in Doñana National Park (Spain).

A cross-sectional study was carried out to evaluate shared pathogens that can be transmitted by close or non-close contact at the domestic-wild ruminants' interface. During summer-autumn 2015, a total of 138 cattle and 203 wild ruminants (red deer, Cervus elaphus, and fallow deer, Dama dama) were sampled in Doñana National Park (DNP, south-western Spain), a Mediterranean ecosystem well known for the interaction network occurring in the ungulate host community. Pestiviruses, bovine respiratory syncytial virus (BRSV; Bovine orthopneumovirus), bovine herpesvirus 1 (BoHV-1; Bovine alphaherpesvirus 1) and Mycobacterium tuberculosis complex (MTC) were assessed using serological, microbiological and molecular techniques. The overall seroprevalence against viruses in cattle was 2.2% for pestiviruses, 11.6% for BRSV and 27.5% for BoHV-1. No virus-specific antibodies were found in wildlife. MTC incidence in cattle was 15.9%, and MTC seroprevalence in wild ruminants was 14.3%. The same Mycobacterium bovis spoligotypes (SB1232, SB1230 and SB1610) were identified in cattle, red deer and fallow deer. The serological results for the selected respiratory viruses suggest epidemiological cycles only in cattle. Surveillance efforts in multi-host epidemiological scenarios are needed to better drive and prioritize control strategies for shared pathogens.

Early life skin microbial trajectory as a function of vertical and environmental transmission in Bornean foam-nesting frogs.

BACKGROUND: The amphibian skin microbiome is an important mediator of host health and serves as a potential source of undiscovered scientifically significant compounds. However, the underlying modalities of how amphibian hosts obtain their initial skin-associated microbiome remains unclear. Here, we explore microbial transmission patterns in foam-nest breeding tree frogs from Southeast Asia (Genus: Polypedates) whose specialized breeding strategy allows for better delineation between vertically and environmentally derived microbes. To facilitate this, we analyzed samples associated with adult frog pairs taken after mating-including adults of each sex, their foam nests, environments, and tadpoles before and after environmental interaction-for the bacterial communities using DNA metabarcoding data (16S rRNA). Samples were collected from frogs in-situ in Brunei, Borneo, a previously unsampled region for amphibian-related microbial diversity. RESULTS: Adult frogs differed in skin bacterial communities among species, but tadpoles did not differ among species. Foam nests had varying bacterial community composition, most notably in the nests' moist interior. Nest interior bacterial communities were discrete for each nest and overall displayed a narrower diversity compared to the nest exteriors. Tadpoles sampled directly from the foam nest displayed a bacterial composition less like the nest interior and more similar to that of the adults and nest exterior. After one week of pond water interaction the tadpole skin microbiome shifted towards the tadpole skin and pond water microbial communities being more tightly coupled than between tadpoles and the internal nest environment, but not to the extent that the skin microbiome mirrored the pond bacterial community. CONCLUSIONS: Both vertical influence and environmental interaction play a role in shaping the tadpole cutaneous microbiome. Interestingly, the interior of the foam nest had a distinct bacterial community from the tadpoles suggesting a limited environmental effect on tadpole cutaneous bacterial selection at initial stages of life. The shift in the tadpole microbiome after environmental interaction indicates an interplay between underlying host and ecological mechanisms that drive community formation. This survey serves as a baseline for further research into the ecology of microbial transmission in aquatic animals.

The Potential Link between Episodes of Diverticulitis or Hemorrhoidal Proctitis and Diets with Selected Plant Foods: A Case-Control Study.

Diverticulitis and hemorrhoidal proctitis in the population are significant public health problems. We studied the potential association between the intake of certain plant foods and diverticulitis or hemorrhoidal episodes through a case-control study including 410 cases and 401 controls. We used a semiquantitative food frequency questionnaire. The intake was additionally quantified according to a 24 h recall. The plant foods or derived food products were categorized by their main chemical components into ethanol, caffeine/theine/theobromine, capsaicin, alliin, acids, eugenol, and miscellaneous foods such as curcumin. The mean score for overall intake of plant foods under consideration was 6.3 points, and this was significantly higher in cases (8.5) than in controls (4.1). Overall intake was similar in cases presenting with diverticulitis or hemorrhoidal proctitis. Cases had 13 times the odds of being in the upper quartile for overall intake (>7 points), compared to controls. Explanatory logistic regression models showed that the strongest association with diverticulitis and hemorrhoidal proctitis was shown by the chemical food group of capsaicin, followed by ethanol, eugenol, caffeine/theine/theobromine, and acids. Neither alliin nor miscellaneous food groups showed any association. High, frequent consumption of capsaicin, followed by ethanol, eugenol, caffeine/theine/theobromine, and acids increase the risk of diverticulitis and hemorrhoidal proctitis.

Afectación renal en el síndrome de Sneddon / Renal involvement in Sneddon síndrome

No disponible

Variation under domestication in animal models: the case of the Mexican axolotl.

BACKGROUND: Species adaptation to laboratory conditions is a special case of domestication that has modified model organisms phenotypically and genetically. The characterisation of these changes is crucial to understand how this variation can affect the outcome of biological experiments. Yet despite the wide use of laboratory animals in biological research, knowledge of the genetic diversity within and between different strains and populations of some animal models is still scarce. This is particularly the case of the Mexican axolotl, which has been bred in captivity since 1864. RESULTS: Using gene expression data from nine different projects, nucleotide sequence variants were characterised, and distinctive genetic background of the experimental specimens was uncovered. This study provides a catalogue of thousands of nucleotide variants along predicted protein-coding genes, while identifying genome-wide differences between pigment phenotypes in laboratory populations. CONCLUSIONS: Awareness of the genetic variation could guide a better experimental design while helping to develop molecular tools for monitoring genetic diversity and studying gene functions in laboratory axolotls. Overall, this study highlights the cross-taxa utility that transcriptomic data might have to assess the genetic variation of the experimental specimens, which might help to shorten the journey towards reproducible research.

Diagnóstico de síndrome de Gitelman en paciente con condrocalcinosis / Diagnosis of gitelman syndrome in patient with condrocalcinosis

RESUMEN Introducción: El síndrome de Gitelman es una tubulopatía caracterizada por alcalosis metabólica hipopotasémica, hipomagnesemia e hipocalciuria. Sus efectos musculoesqueléticos son comunes, pudiendo provocar desarrollo de condrocalcinosis. Caso clínico: Paciente con condrocalcinosis de larga data asociada a hipomagnesemia crónica en tratamiento con calcio y magnesio. Tras la suspensión del tratamiento debido a una intervención quirúrgica presentó debilidad generalizada, alcalosis metabólica, hipopotasemia, hipomagnesemia e hipocalciuria con diagnóstico final de síndrome de Gitelman. Tras la instauración de tratamiento, mejoró clínica y analíticamente manteniendo cifras iónicas estables. Discusión y conclusiones: Resulta fundamental un adecuado diagnóstico de este tipo de tubulopatías, ya que un tratamiento adecuado evita complicaciones asociadas.

ABSTRACT Introduction: Gitelman syndrome is a renal tubule disease that involves hypokalaemic metabolic alkalosis, hypomagnesaemia and hypocalciuria. The musculoskeletal effects of Gitelman syndrome are common, including the development of chondrocalcinosis. Clinical case: A female patient with long-standing chondrocalcinosis associated with chronic hypomagnesaemia on treatment with calcium and magnesium. After the suspension of the treatment due to surgery, she presented with a generalised weakness, metabolic alkalosis, hypokalaemia, hypomagnesaemia and hypocalciuria, with final diagnosis of Gitelman syndrome. After re-introducing the treatment, she improved clinically, with electrolytes remaining stable. Discussion and conclusions: A proper diagnosis of this type of tubular diseases is essential because an adequate treatment avoids associated complications.

Insights into the skin of caecilian amphibians from gene expression profiles.

BACKGROUND: Gene expression profiles can provide insights into the molecular machinery behind tissue functions and, in turn, can further our understanding of environmental responses, and developmental and evolutionary processes. During vertebrate evolution, the skin has played a crucial role, displaying a wide diversity of essential functions. To unravel the molecular basis of skin specialisations and adaptations, we compared gene expression in the skin with eight other tissues in a phylogenetically and ecologically diverse species sample of one of the most neglected vertebrate groups, the caecilian amphibians (order Gymnophiona). RESULTS: The skin of the five studied caecilian species showed a distinct gene expression profile reflecting its developmental origin and showing similarities to other epithelial tissues. We identified 59 sequences with conserved enhanced expression in the skin that might be associated with caecilian dermal specialisations. Some of the up-regulated genes shared expression patterns with human skin and potentially are involved in skin functions across vertebrates. Variation trends in gene expression were detected between mid and posterior body skin suggesting different functions between body regions. Several candidate biologically active peptides were also annotated. CONCLUSIONS: Our study provides the first atlas of differentially expressed sequences in caecilian tissues and a baseline to explore the molecular basis of the skin functions in caecilian amphibians, and more broadly in vertebrates.

What lies beneath? Molecular evolution during the radiation of caecilian amphibians.

BACKGROUND: Evolution leaves an imprint in species through genetic change. At the molecular level, evolutionary changes can be explored by studying ratios of nucleotide substitutions. The interplay among molecular evolution, derived phenotypes, and ecological ranges can provide insights into adaptive radiations. Caecilians (order Gymnophiona), probably the least known of the major lineages of vertebrates, are limbless tropical amphibians, with adults of most species burrowing in soils (fossoriality). This enigmatic order of amphibians are very distinct phenotypically from other extant amphibians and likely from the ancestor of Lissamphibia, but little to nothing is known about the molecular changes underpinning their radiation. We hypothesised that colonization of various depths of tropical soils and of freshwater habitats presented new ecological opportunities to caecilians. RESULTS: A total of 8540 candidate groups of orthologous genes from transcriptomic data of five species of caecilian amphibians and the genome of the frog Xenopus tropicalis were analysed in order to investigate the genetic machinery behind caecilian diversification. We found a total of 168 protein-coding genes with signatures of positive selection at different evolutionary times during the radiation of caecilians. The majority of these genes were related to functional elements of the cell membrane and extracellular matrix with expression in several different tissues. The first colonization of the tropical soils was connected to the largest number of protein-coding genes under positive selection in our analysis. From the results of our study, we highlighted molecular changes in genes involved in perception, reduction-oxidation processes, and aging that likely were involved in the adaptation to different soil strata. CONCLUSIONS: The genes inferred to have been under positive selection provide valuable insights into caecilian evolution, potentially underpin adaptations of caecilians to their extreme environments, and contribute to a better understanding of fossorial adaptations and molecular evolution in vertebrates.

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.

Multi-tissue transcriptomes of caecilian amphibians highlight incomplete knowledge of vertebrate gene families.

RNA sequencing (RNA-seq) has become one of the most powerful tools to unravel the genomic basis of biological adaptation and diversity. Although challenging, RNA-seq is particularly promising for research on non-model, secretive species that cannot be observed in nature easily and therefore remain comparatively understudied. Among such animals, the caecilians (order Gymnophiona) likely constitute the least known group of vertebrates, despite being an old and remarkably distinct lineage of amphibians. Here, we characterize multi-tissue transcriptomes for five species of caecilians that represent a broad level of diversity across the order. We identified vertebrate homologous elements of caecilian functional genes of varying tissue specificity that reveal a great number of unclassified gene families, especially for the skin. We annotated several protein domains for those unknown candidate gene families to investigate their function. We also conducted supertree analyses of a phylogenomic dataset of 1,955 candidate orthologous genes among five caecilian species and other major lineages of vertebrates, with the inferred tree being in agreement with current views of vertebrate evolution and systematics. Our study provides insights into the evolution of vertebrate protein-coding genes, and a basis for future research on the molecular elements underlying the particular biology and adaptations of caecilian amphibians.

Molecular evolution of DNMT1 in vertebrates: Duplications in marsupials followed by positive selection.

DNA methylation is mediated by a conserved family of DNA methyltransferases (Dnmts). The human genome encodes three active Dnmts (Dnmt1, Dnmt3a and Dnmt3b), the tRNA methyltransferase Dnmt2, and the regulatory protein Dnmt3L. Despite their high degree of conservation among different species, genes encoding Dnmts have been duplicated and/or lost in multiple lineages throughout evolution, indicating that the DNA methylation machinery has some potential to undergo evolutionary change. However, little is known about the extent to which this machinery, or the methylome, varies among vertebrates. Here, we study the molecular evolution of Dnmt1, the enzyme responsible for maintenance of DNA methylation patterns after replication, in 79 vertebrate species. Our analyses show that all studied species exhibit a single copy of the DNMT1 gene, with the exception of tilapia and marsupials (tammar wallaby, koala, Tasmanian devil and opossum), each of which displays two apparently functional DNMT1 copies. Our phylogenetic analyses indicate that DNMT1 duplicated before the radiation of major marsupial groups (i.e., at least ~75 million years ago), thus giving rise to two DNMT1 copies in marsupials (copy 1 and copy 2). In the opossum lineage, copy 2 was lost, and copy 1 recently duplicated again, generating three DNMT1 copies: two putatively functional genes (copy 1a and 1b) and one pseudogene (copy 1ψ). Both marsupial copies (DNMT1 copies 1 and 2) are under purifying selection, and copy 2 exhibits elevated rates of evolution and signatures of positive selection, suggesting a scenario of neofunctionalization. This gene duplication might have resulted in modifications in marsupial methylomes and their dynamics.