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Natural populations subjected to strong environmental selection pressures offer a window into the genetic underpinnings of evolutionary change. Cavefish populations, Astyanax mexicanus (Teleostei: Characiphysi), exhibit repeated, independent evolution for a variety of traits including eye degeneration, pigment loss, increased size and number of taste buds and mechanosensory organs, and shifts in many behavioural traits. Surface and cave forms are interfertile making this system amenable to genetic interrogation; however, lack of a reference genome has hampered efforts to identify genes responsible for changes in cave forms of A. mexicanus. Here we present the first de novo genome assembly for Astyanax mexicanus cavefish, contrast repeat elements to other teleost genomes, identify candidate genes underlying quantitative trait loci (QTL), and assay these candidate genes for potential functional and expression differences. We expect the cavefish genome to advance understanding of the evolutionary process, as well as, analogous human disease including retinal dysfunction. Populations of the cave fish Astyanax mexicanus exhibit a variety of traits that evolved repeatedly and independently from its surface counterparts. Here the authors present a de novo genome assembly for A. mexicanus and identify candidate genes for eye loss and reduced pigmentation.

Naoki Irie and colleagues report the draft genomes of the soft-shell and green sea turtles. Their genome-wide phylogenetic analysis supports the hypothesis that turtles are a sister group of crocodilians and birds. The unique anatomical features of turtles have raised unanswered questions about the origin of their unique body plan. We generated and analyzed draft genomes of the soft-shell turtle ( Pelodiscus sinensis ) and the green sea turtle ( Chelonia mydas ); our results indicated the close relationship of the turtles to the bird-crocodilian lineage, from which they split ∼267.9–248.3 million years ago (Upper Permian to Triassic). We also found extensive expansion of olfactory receptor genes in these turtles. Embryonic gene expression analysis identified an hourglass-like divergence of turtle and chicken embryogenesis, with maximal conservation around the vertebrate phylotypic period, rather than at later stages that show the amniote-common pattern. Wnt5a expression was found in the growth zone of the dorsal shell, supporting the possible co-option of limb-associated Wnt signaling in the acquisition of this turtle-specific novelty. Our results suggest that turtle evolution was accompanied by an unexpectedly conservative vertebrate phylotypic period, followed by turtle-specific repatterning of development to yield the novel structure of the shell.

The RGASP consortium compared 25 RNA-seq analysis programs in their ability to identify exons, reconstruct transcripts and quantify expression levels. Assembly of isoforms and their expression levels in higher eukaryotes remains a challenge. We evaluated 25 protocol variants of 14 independent computational methods for exon identification, transcript reconstruction and expression-level quantification from RNA-seq data. Our results show that most algorithms are able to identify discrete transcript components with high success rates but that assembly of complete isoform structures poses a major challenge even when all constituent elements are identified. Expression-level estimates also varied widely across methods, even when based on similar transcript models. Consequently, the complexity of higher eukaryotic genomes imposes severe limitations on transcript recall and splice product discrimination that are likely to remain limiting factors for the analysis of current-generation RNA-seq data.

Wesley Warren and colleagues report the whole-genome sequence of the platyfish, Xiphophorus maculatus , providing the first genome of a poeciliid fish. They provide a resource for this model organism used to study traits including viviparity, complex behaviors, pigmentation and cancer, and their comparative analysis provides insights into evolutionary adaptations in natural teleost populations. Several attributes intuitively considered to be typical mammalian features, such as complex behavior, live birth and malignant disease such as cancer, also appeared several times independently in lower vertebrates. The genetic mechanisms underlying the evolution of these elaborate traits are poorly understood. The platyfish, X. maculatus , offers a unique model to better understand the molecular biology of such traits. We report here the sequencing of the platyfish genome. Integrating genome assembly with extensive genetic maps identified an unexpected evolutionary stability of chromosomes in fish, in contrast to in mammals. Genes associated with viviparity show signatures of positive selection, identifying new putative functional domains and rare cases of parallel evolution. We also find that genes implicated in cognition show an unexpectedly high rate of duplicate gene retention after the teleost genome duplication event, suggesting a hypothesis for the evolution of the behavioral complexity in fish, which exceeds that found in amphibians and reptiles.

The genetic changes underlying the initial steps of animal domestication are still poorly understood. We generated a high-quality reference genome for the rabbit and compared it to resequencing data from populations of wild and domestic rabbits. We identified more than 100 selective sweeps specific to domestic rabbits but only a relatively small number of fixed (or nearly fixed) single-nucleotide polymorphisms (SNPs) for derived alleles. SNPs with marked allele frequency differences between wild and domestic rabbits were enriched for conserved noncoding sites. Enrichment analyses suggest that genes affecting brain and neuronal development have often been targeted during domestication. We propose that because of a truly complex genetic background, tame behavior in rabbits and other domestic animals evolved by shifts in allele frequencies at many loci, rather than by critical changes at only a few domestication loci.

Cod goes its own way on immunity The genome of the Atlantic cod has been sequenced, and genomic analysis reveals an immune system that differs significantly from that in other vertebrates. The major histocompatibility complex (MHC) II has been lost, as have some other genes that are essential for MHC II function. But there is an expansion in the number of MHC I genes and a unique composition for its toll-like receptor family. These compensatory changes in both adaptive and innate immunity mean that cod is no more susceptible to disease than most other vertebrates. These findings challenge current models of vertebrate immune evolution, and may facilitate the development of targeted vaccines for disease management in aquaculture. Atlantic cod ( Gadus morhua ) is a large, cold-adapted teleost that sustains long-standing commercial fisheries and incipient aquaculture 1 , 2 . Here we present the genome sequence of Atlantic cod, showing evidence for complex thermal adaptations in its haemoglobin gene cluster and an unusual immune architecture compared to other sequenced vertebrates. The genome assembly was obtained exclusively by 454 sequencing of shotgun and paired-end libraries, and automated annotation identified 22,154 genes. The major histocompatibility complex (MHC) II is a conserved feature of the adaptive immune system of jawed vertebrates 3 , 4 , but we show that Atlantic cod has lost the genes for MHC II, CD4 and invariant chain (Ii) that are essential for the function of this pathway. Nevertheless, Atlantic cod is not exceptionally susceptible to disease under natural conditions 5 . We find a highly expanded number of MHC I genes and a unique composition of its Toll-like receptor (TLR) families. This indicates how the Atlantic cod immune system has evolved compensatory mechanisms in both adaptive and innate immunity in the absence of MHC II. These observations affect fundamental assumptions about the evolution of the adaptive immune system and its components in vertebrates.

Community acquired pneumonia is a common condition that causes considerable morbidity and has a mortality rate of approximately 20% for patients admitted to hospital in the United Kingdom. 1 It is diagnosed in 5-12% of adults who present to general practitioners with symptoms of lower respiratory tract infection, 2 3 and 22-42% are subsequently admitted to hospital. 3 4 Adherence to previous guidelines has been poor, and this variation in practice can lead to suboptimal outcomes such as increased mortality and longer stay in hospital. 5 6 7 Hospital acquired pneumonia (excluding ventilator associated pneumonia) has a point prevalence of approximately 1% of hospital inpatients, is estimated to lengthen hospital admission by an average of eight days, and has a high mortality rate. 8 9 This article summarises the most recent recommendations for the management of both types of pneumonia from the National Institute for Health and Care Excellence (NICE). Confusion (abbreviated mental test score 8 or less or new disorientation in person, place, or time)* Raised blood urea nitrogen (over 7 mmol/L) Raised respiratory rate (30 breaths per minute or more) Low blood pressure (diastolic 60 mm Hg or less, or systolic less than 90 mm Hg) Age 65 years or more Patients are stratified for risk of death as follows: 0 or 1=low risk (less than 3% mortality risk) 2=intermediate risk (3 to 15% mortality risk) 3 to 5=high risk (more than 15% mortality risk) *For guidance on delirium, please refer to National Institute for Health and Care Excellence.

Ning Li and colleagues report the whole-genome sequence of the duck, Anas platyrhynchos , a natural host of avian influenza viruses. They examine host response to infection by comparing the lung transcriptomes of ducks that were infected with influenza A viruses. The duck ( Anas platyrhynchos ) is one of the principal natural hosts of influenza A viruses. We present the duck genome sequence and perform deep transcriptome analyses to investigate immune-related genes. Our data indicate that the duck possesses a contractive immune gene repertoire, as in chicken and zebra finch, and this repertoire has been shaped through lineage-specific duplications. We identify genes that are responsive to influenza A viruses using the lung transcriptomes of control ducks and ones that were infected with either a highly pathogenic (A/duck/Hubei/49/05) or a weakly pathogenic (A/goose/Hubei/65/05) H5N1 virus. Further, we show how the duck's defense mechanisms against influenza infection have been optimized through the diversification of its β-defensin and butyrophilin-like repertoires. These analyses, in combination with the genomic and transcriptomic data, provide a resource for characterizing the interaction between host and influenza viruses.

The genome sequence of the ferret, a model of human respiratory disease, enables research on influenza and cystic fibrosis. The domestic ferret ( Mustela putorius furo ) is an important animal model for multiple human respiratory diseases. It is considered the 'gold standard' for modeling human influenza virus infection and transmission 1 , 2 , 3 , 4 . Here we describe the 2.41 Gb draft genome assembly of the domestic ferret, constituting 2.28 Gb of sequence plus gaps. We annotated 19,910 protein-coding genes on this assembly using RNA-seq data from 21 ferret tissues. We characterized the ferret host response to two influenza virus infections by RNA-seq analysis of 42 ferret samples from influenza time-course data and showed distinct signatures in ferret trachea and lung tissues specific to 1918 or 2009 human pandemic influenza virus infections. Using microarray data from 16 ferret samples reflecting cystic fibrosis disease progression, we showed that transcriptional changes in the CFTR-knockout ferret lung reflect pathways of early disease that cannot be readily studied in human infants with cystic fibrosis disease.