RESUMO
The freshwater cnidarian Hydra was first described in 1702 and has been the object of study for 300 years. Experimental studies of Hydra between 1736 and 1744 culminated in the discovery of asexual reproduction of an animal by budding, the first description of regeneration in an animal, and successful transplantation of tissue between animals. Today, Hydra is an important model for studies of axial patterning, stem cell biology and regeneration. Here we report the genome of Hydra magnipapillata and compare it to the genomes of the anthozoan Nematostella vectensis and other animals. The Hydra genome has been shaped by bursts of transposable element expansion, horizontal gene transfer, trans-splicing, and simplification of gene structure and gene content that parallel simplification of the Hydra life cycle. We also report the sequence of the genome of a novel bacterium stably associated with H. magnipapillata. Comparisons of the Hydra genome to the genomes of other animals shed light on the evolution of epithelia, contractile tissues, developmentally regulated transcription factors, the Spemann-Mangold organizer, pluripotency genes and the neuromuscular junction.
Assuntos
Genoma/genética , Hydra/genética , Animais , Antozoários/genética , Comamonadaceae/genética , Elementos de DNA Transponíveis/genética , Transferência Genética Horizontal/genética , Genoma Bacteriano/genética , Hydra/microbiologia , Hydra/ultraestrutura , Dados de Sequência Molecular , Junção Neuromuscular/ultraestruturaRESUMO
Scientists working with single-nucleotide variants (SNVs), inferred by next-generation sequencing software, often need further information regarding true variants, artifacts and sequence coverage gaps. In clinical diagnostics, e.g. SNVs must usually be validated by visual inspection or several independent SNV-callers. We here demonstrate that 0.5-60% of relevant SNVs might not be detected due to coverage gaps, or might be misidentified. Even low error rates can overwhelm the true biological signal, especially in clinical diagnostics, in research comparing healthy with affected cells, in archaeogenetic dating or in forensics. For these reasons, we have developed a package called pibase, which is applicable to diploid and haploid genome, exome or targeted enrichment data. pibase extracts details on nucleotides from alignment files at user-specified coordinates and identifies reproducible genotypes, if present. In test cases pibase identifies genotypes at 99.98% specificity, 10-fold better than other tools. pibase also provides pair-wise comparisons between healthy and affected cells using nucleotide signals (10-fold more accurately than a genotype-based approach, as we show in our case study of monozygotic twins). This comparison tool also solves the problem of detecting allelic imbalance within heterozygous SNVs in copy number variation loci, or in heterogeneous tumor sequences.
Assuntos
Variação Genética , Sequenciamento de Nucleotídeos em Larga Escala , Alinhamento de Sequência , Análise de Sequência de DNA , Software , Genômica , Humanos , Filogenia , Reprodutibilidade dos Testes , Gêmeos Monozigóticos/genéticaRESUMO
Hydra's unlimited life span has long attracted attention from natural scientists. The reason for that phenomenon is the indefinite self-renewal capacity of its stem cells. The underlying molecular mechanisms have yet to be explored. Here, by comparing the transcriptomes of Hydra's stem cells followed by functional analysis using transgenic polyps, we identified the transcription factor forkhead box O (FoxO) as one of the critical drivers of this continuous self-renewal. foxO overexpression increased interstitial stem cell and progenitor cell proliferation and activated stem cell genes in terminally differentiated somatic cells. foxO down-regulation led to an increase in the number of terminally differentiated cells, resulting in a drastically reduced population growth rate. In addition, it caused down-regulation of stem cell genes and antimicrobial peptide (AMP) expression. These findings contribute to a molecular understanding of Hydra's immortality, indicate an evolutionarily conserved role of FoxO in controlling longevity from Hydra to humans, and have implications for understanding cellular aging.
Assuntos
Fatores de Transcrição Forkhead/fisiologia , Hydra/citologia , Células-Tronco/metabolismo , Animais , Animais Geneticamente Modificados , Linhagem da Célula , Fatores de Transcrição Forkhead/genética , Inativação Gênica , Hydra/imunologia , Hydra/metabolismo , Imunidade Inata , Dados de Sequência MolecularRESUMO
How distinct stem cell populations originate and whether there is a clear stem cell "genetic signature" remain poorly understood. Understanding the evolution of stem cells requires molecular profiling of stem cells in an animal at a basal phylogenetic position. In this study, using transgenic Hydra polyps, we reveal for each of the three stem cell populations a specific signature set of transcriptions factors and of genes playing key roles in cell type-specific function and interlineage communication. Our data show that principal functions of stem cell genes, such as maintenance of stemness and control of stem cell self-renewal and differentiation, arose very early in metazoan evolution. They are corroborating the view that stem cell types shared common, multifunctional ancestors, which achieved complexity through a stepwise segregation of function in daughter cells.
Assuntos
Linhagem da Célula/genética , Perfilação da Expressão Gênica , Hydra/citologia , Hydra/genética , Células-Tronco/citologia , Células-Tronco/metabolismo , Animais , Evolução Biológica , Separação Celular , Regulação da Expressão Gênica , Teste de Complementação Genética , Camundongos , Filogenia , Coloração e Rotulagem , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Transcriptoma/genéticaRESUMO
Taxonomically restricted genes or lineage-specific genes contribute to morphological diversification in metazoans and provide unique functions for particular taxa in adapting to specific environments. To understand how such genes arise and participate in morphological evolution, we have investigated a gene called nematogalectin in Hydra, which has a structural role in the formation of nematocysts, stinging organelles that are unique to the phylum Cnidaria. Nematogalectin is a 28-kDa protein with an N-terminal GlyXY domain (glycine followed by two hydrophobic amino acids), which can form a collagen triple helix, followed by a galactose-binding lectin domain. Alternative splicing of the nematogalectin transcript allows the gene to encode two proteins, nematogalectin A and nematogalectin B. We demonstrate that expression of nematogalectin A and B is mutually exclusive in different nematocyst types: Desmonemes express nematogalectin B, whereas stenoteles and isorhizas express nematogalectin B early in differentiation, followed by nematogalectin A. Like Hydra, the marine hydrozoan Clytia also has two nematogalectin transcripts, which are expressed in different nematocyte types. By comparison, anthozoans have only one nematogalectin gene. Gene phylogeny indicates that tandem duplication of nematogalectin B exons gave rise to nematogalectin A before the divergence of Anthozoa and Medusozoa and that nematogalectin A was subsequently lost in Anthozoa. The emergence of nematogalectin A may have played a role in the morphological diversification of nematocysts in the medusozoan lineage.
Assuntos
Galectinas/química , Galectinas/genética , Hydra/genética , Hydra/metabolismo , Processamento Alternativo , Sequência de Aminoácidos , Animais , Sequência de Bases , Cnidários/classificação , Cnidários/genética , Sequência Conservada , Primers do DNA/genética , Evolução Molecular , Galectinas/metabolismo , Hydra/crescimento & desenvolvimento , Imuno-Histoquímica , Hibridização In Situ , Dados de Sequência Molecular , Estrutura Terciária de Proteína , Homologia de Sequência de AminoácidosRESUMO
Members of the universal stress protein (USP) family were originally identified in stressed bacteria on the basis of a shared domain, which has since been reported in a phylogenetically diverse range of prokaryotes, fungi, protists, and plants. Although not previously characterized in metazoans, here we report that USP genes are distributed in animal genomes in a unique pattern that reflects frequent independent losses and independent expansions. Multiple USP loci are present in urochordates as well as all Cnidaria and Lophotrochozoa examined, but none were detected in any of the available ecdysozoan or non-urochordate deuterostome genome data. The vast majority of the metazoan USPs are short, single-domain proteins and are phylogenetically distinct from the prokaryotic, plant, protist, and fungal members of the protein family. Whereas most of the metazoan USP genes contain introns, with few exceptions those in the cnidarian Hydra are intronless and cluster together in phylogenetic analyses. Expression patterns were determined for several cnidarian USPs, including two genes belonging to the intronless clade, and these imply diverse functions. The apparent paradox of implied diversity of roles despite high overall levels of sequence (and implied structural) similarity parallels the situation in bacteria. The absence of USP genes in ecdysozoans and most deuterostomes may be a consequence of functional redundancy or specialization in taxon-specific roles.
Assuntos
Genômica/métodos , Proteínas de Choque Térmico/genética , Filogenia , Sequência de Aminoácidos , Animais , Teorema de Bayes , Expressão Gênica , Proteínas de Choque Térmico/classificação , Humanos , Hydra/anatomia & histologia , Hydra/classificação , Hydra/genética , Hibridização In Situ , Dados de Sequência Molecular , Alinhamento de SequênciaRESUMO
Distinguishing self from nonself and the onset of defense effector mechanisms upon recognition of pathogens are essential for the survival of all life forms in the animal kingdom. The family of nucleotide -binding and oligomeriszation domain-like receptors (NLRs) was first identified in vertebrates and comprises a group of pivotal sensor protein of the innate immune system for microbial cell wall components or danger signals. Here, we provide first evidence that early diverging metazoans have large and complex NLR repertoires. The cnidarian NACHT/NB-ARC genes include novel combinations of domains, and the number of one specific type (NB-ARC and tetratricopeptide repeat containing) in Hydra is particularly large. We characterize the transcript structure and expression patterns of a selected HyNLR, HyNLR type 1 and describe putative interaction partners. In a heterologous expression system, we show induced proximity recruitment of an effector caspase (HyDD-Caspase) to the HyNLR type 1 protein upon oligomerization indicating a potential role of caspase activation downstream of NLR activation in Hydra. These results add substantially to our understanding of the ancestral innate immune repertoire as well as providing the first insights into putative cytoplasmic defense mechanisms at the base of animal evolution.
Assuntos
Evolução Molecular , Hydra/genética , Proteínas Adaptadoras de Sinalização NOD/genética , Sequência de Aminoácidos , Animais , Caspases/metabolismo , Simulação por Computador , Componentes do Gene , Perfilação da Expressão Gênica , Humanos , Hydra/imunologia , Imunidade Inata , Modelos Genéticos , Proteínas Adaptadoras de Sinalização NOD/química , Filogenia , Ligação Proteica , Mapeamento de Interação de Proteínas , Estrutura Terciária de Proteína , Análise de Sequência de DNA , Transcrição GênicaRESUMO
Comparative genome analyses indicate that every taxonomic group so far studied contains 10-20% of genes that lack recognizable homologs in other species. Do such 'orphan' or 'taxonomically-restricted' genes comprise spurious, non-functional ORFs, or does their presence reflect important evolutionary processes? Recent studies in basal metazoans such as Nematostella, Acropora and Hydra have shed light on the function of these genes, and now indicate that they are involved in important species-specific adaptive processes. Here we focus on evidence from Hydra suggesting that taxonomically-restricted genes play a role in the creation of phylum-specific novelties such as cnidocytes, in the generation of morphological diversity, and in the innate defence system. We propose that taxon-specific genes drive morphological specification, enabling organisms to adapt to changing conditions.
Assuntos
Adaptação Biológica/genética , Evolução Molecular , Genes , Hydra/genética , Filogenia , Animais , Bactérias/genética , Variação Genética , Humanos , Hydra/anatomia & histologia , Hydra/classificação , Especificidade da Espécie , Leveduras/genéticaRESUMO
Understanding the molecular events that underlie the evolution of morphological diversity is a major challenge in biology. Here, to identify genes whose expression correlates with species-specific morphologies, we compared transcriptomes of two closely related Hydra species. We find that species-specific differences in tentacle formation correlate with expression of a taxonomically restricted gene encoding a small secreted protein. We show that gain of function induces changes in morphology that mirror the phenotypic differences observed between species. These results suggest that "novel" genes may be involved in the generation of species-specific morphological traits.
Assuntos
Evolução Molecular , Regulação da Expressão Gênica no Desenvolvimento , Hydra/genética , Fatores de Transcrição/genética , Sequência de Aminoácidos , Animais , Expressão Gênica , Inativação Gênica , Hydra/anatomia & histologia , Hydra/classificação , Hibridização In Situ , Dados de Sequência Molecular , Fenótipo , Filogenia , Alinhamento de Sequência , Especificidade da EspécieRESUMO
Hydra is a powerful stem cell model because its potential immortality and extensive regeneration capacity is due to the presence of three distinct stem cell lineages. All three lineages conform to a well-defined spatial distribution across the whole body column of the polyp. Stem cell function in Hydra is controlled by extracellular cues and intrinsic genetic programs. This review focuses on the elusive stem cell niche of the epithelial layers. Based on a comparison of the differences between, and commonalities among, stem cells and stem cell niches in Hydra and other invertebrates and vertebrates, we propose that the whole body column of the polyp may be considered a stem cell "niche" in which stem cell populations are established and signals ensuring the proper balance between stem cells and progenitor cells are integrated. We show that, at over 500 million years old, Hydra offers an early glimpse of the regulatory potential of stem cell niches.
Assuntos
Diferenciação Celular , Células Epiteliais/citologia , Hydra/citologia , Células-Tronco/citologia , Animais , Células Epiteliais/metabolismo , Hydra/metabolismo , Hydra/fisiologia , Modelos Biológicos , Regeneração/fisiologia , Transdução de Sinais , Nicho de Células-Tronco/citologia , Nicho de Células-Tronco/metabolismo , Células-Tronco/metabolismo , Proteínas Wnt/metabolismoRESUMO
Large-scale species comparisons at genome and expressed sequence tag (EST) levels have revealed that early branching metazoans such as sponges and cnidarians share many if not most of their genes with the allegedly advanced vertebrates including man. The ancestor of all animals may thus have been much more complex than anticipated. To facilitate and support analysis of genomic and transcriptomic resources in early branching metazoans, we have established a local bio-computational platform, Compagen (http://www.compagen.org). The platform contains searchable databases with selected raw genomic and EST sequence datasets from sponges and cnidarians up to the lower vertebrates. In addition to the public datasets, Compagen also provides processed data like CAP3 assembled ESTs or predicted peptides. Evaluating the efficacy of the platform by screening for genes reported to be essential in controlling stem-cell behavior in higher organisms uncovered ancient origins for some but not all components of the vertebrate stem-cell system.
Assuntos
Diferenciação Celular/genética , Bases de Dados Genéticas , Regulação da Expressão Gênica no Desenvolvimento , Genômica , Células-Tronco/citologia , Animais , Cnidários/genética , Biologia Computacional , Evolução Molecular , Etiquetas de Sequências Expressas , Perfilação da Expressão Gênica , Poríferos/genéticaRESUMO
The emergence of multidrug-resistant bacteria highlights the need for new antibacterial agents. Arminin 1a is a novel antimicrobial peptide discovered during investigations of the epithelial defense of the ancient metazoan Hydra. Following proteolytic processing, the 31-amino-acid-long positively charged C-terminal part of arminin 1a exhibits potent and broad-spectrum activity against bacteria, including multiresistant human pathogenic strains, such as methicillin-resistant Staphylococcus aureus (MRSA) strains (minimal bactericidal concentration, 0.4 microM to 0.8 microM). Ultrastructural observations indicate that bacteria are killed by disruption of the bacterial cell wall. Remarkably, the antibacterial activity of arminin 1a is not affected under the physiological salt conditions of human blood. In addition, arminin 1a is a selective antibacterial agent that does not affect human erythrocyte membranes. Arminin 1a shows no sequence homology to any known antimicrobial peptide. Because of its high level of activity against multiresistant bacterial strains pathogenic for humans, the peptide arminin 1a is a promising template for a new class of antibiotics. Our data suggest that ancient metazoan organisms such as Hydra hold promise for the detection of novel antimicrobial molecules and the treatment of infections caused by multiresistant bacteria.
Assuntos
Antibacterianos/farmacologia , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Peptídeos/farmacologia , Sequência de Aminoácidos , Antibacterianos/efeitos adversos , Antibacterianos/química , Parede Celular/efeitos dos fármacos , Parede Celular/ultraestrutura , Biologia Computacional , Farmacorresistência Bacteriana Múltipla/efeitos dos fármacos , Eritrócitos/efeitos dos fármacos , Hemólise/efeitos dos fármacos , Humanos , Hibridização In Situ , Staphylococcus aureus Resistente à Meticilina/ultraestrutura , Testes de Sensibilidade Microbiana , Microscopia Eletrônica de Transmissão , Dados de Sequência Molecular , Peptídeos/efeitos adversos , Peptídeos/química , Peptídeos/classificação , Filogenia , Homologia de Sequência de AminoácidosRESUMO
The evolutionary origin of allorecognition in vertebrates is unknown. Urochordates, being the closest living relatives of vertebrates [Delsuc F, Brinkmann H, Chourrout D, Philippe H]. Tunicates and not cephalochordates are the closest living relatives of vertebrates. Nature 2006; 439: 965-8], have efficient mechanisms to prevent both allogeneic fusion and self fertilization. To shed light on allorecognition in urochordates and on the molecules involved in preventing self fertilization, we compared gonadal cDNAs of three genetically unrelated Ciona intestinalis individuals by suppression subtractive hybridisation (SSH). Here, we report the discovery and characterization of a highly polymorphic gene coding for a transmembrane protein with several short consensus repeat domains (SCR/CCP). The protein, termed variable complement receptor-like 1 (vCRL1), is structurally similar to vertebrate complement receptors. However, in contrast to vertebrate complement receptors, vCRL1 shows an unprecedented high degree of amino acid variations among Ciona individuals and is expressed in follicle cells as well as in hemocytes. Based on our data we propose that in the absence of MHC Ciona uses variable components of the complement system as individuality markers.
Assuntos
Ciona intestinalis/imunologia , Variação Genética , Folículo Ovariano/imunologia , Receptores de Complemento/isolamento & purificação , Sequência de Aminoácidos , Animais , Sequência de Bases , Ciona intestinalis/metabolismo , Evolução Molecular , Feminino , Marcadores Genéticos , Dados de Sequência Molecular , Folículo Ovariano/química , Folículo Ovariano/metabolismo , Receptores de Complemento/biossíntese , Receptores de Complemento/genéticaRESUMO
Several pathogenic viruses such as hepatitis B and human immunodeficiency viruses may integrate into the host genome. These virus/host integrations are detectable using paired-end next generation sequencing. However, the low number of expected true virus integrations may be difficult to distinguish from the noise of many false positive candidates. Here, we propose a novel filtering approach that increases specificity without compromising sensitivity for virus/host chimera detection. Our detection pipeline termed Vy-PER (Virus integration detection bY Paired End Reads) outperforms existing similar tools in speed and accuracy. We analysed whole genome data from childhood acute lymphoblastic leukemia (ALL), which is characterised by genomic rearrangements and usually associated with radiation exposure. This analysis was motivated by the recently reported virus integrations at genomic rearrangement sites and association with chromosomal instability in liver cancer. However, as expected, our analysis of 20 tumour and matched germline genomes from ALL patients finds no significant evidence for integrations by known viruses. Nevertheless, our method eliminates 12,800 false positives per genome (80× coverage) and only our method detects singleton human-phiX174-chimeras caused by optical errors of the Illumina HiSeq platform. This high accuracy is useful for detecting low virus integration levels as well as non-integrated viruses.
Assuntos
Biologia Computacional , Software , Reações Falso-Positivas , Genoma Humano , Células Germinativas/metabolismo , Vírus da Hepatite B/genética , Vírus da Hepatite B/fisiologia , Herpesviridae/genética , Herpesviridae/fisiologia , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Neoplasias Hepáticas/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras/virologia , Análise de Sequência de DNA , Integração ViralRESUMO
BACKGROUND: The life cycle of scyphozoan cnidarians alternates between sessile asexual polyps and pelagic medusa. Transition from one life form to another is triggered by environmental signals, but the molecular cascades involved in the drastic morphological and physiological changes remain unknown. RESULTS: We show in the moon jelly Aurelia aurita that the molecular machinery controlling transition of the sessile polyp into a free-swimming jellyfish consists of two parts. One is conserved and relies on retinoic acid signaling. The second, novel part is based on secreted proteins that are strongly upregulated prior to metamorphosis in response to the seasonal temperature changes. One of these proteins functions as a temperature-sensitive "timer" and encodes the precursor of the strobilation hormone of Aurelia. CONCLUSIONS: Our findings uncover the molecule framework controlling the polyp-to-jellyfish transition in a basal metazoan and provide insights into the evolution of complex life cycles in the animal kingdom.
Assuntos
Hormônios/fisiologia , Estágios do Ciclo de Vida/fisiologia , Metamorfose Biológica/fisiologia , Cifozoários/crescimento & desenvolvimento , Animais , Hibridização In Situ , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da PolimeraseRESUMO
BACKGROUND: Despite decades of research, the molecular mechanisms responsible for the evolution of morphological diversity remain poorly understood. While current models assume that species-specific morphologies are governed by differential use of conserved genetic regulatory circuits, it is debated whether non-conserved taxonomically restricted genes are also involved in making taxonomically relevant structures. The genomic resources available in Hydra, a member of the early branching animal phylum Cnidaria, provide a unique opportunity to study the molecular evolution of morphological novelties such as the nematocyte, a cell type characteristic of, and unique to, Cnidaria. RESULTS: We have identified nematocyte-specific genes by suppression subtractive hybridization and find that a considerable portion has no homologues to any sequences in animals outside Hydra. By analyzing the transcripts of these taxonomically restricted genes and mining of the Hydra magnipapillata genome, we find unexpected complexity in gene structure and transcript processing. Transgenic Hydra expressing the green fluorescent protein reporter under control of one of the taxonomically restricted gene promoters recapitulate faithfully the described expression pattern, indicating that promoters of taxonomically restricted genes contain all elements essential for spatial and temporal control mechanisms. Surprisingly, phylogenetic footprinting of this promoter did not reveal any conserved cis-regulatory elements. CONCLUSIONS: Our findings suggest that taxonomically restricted genes are involved in the evolution of morphological novelties such as the cnidarian nematocyte. The transcriptional regulatory network controlling taxonomically restricted gene expression may contain not yet characterized transcription factors or cis-regulatory elements.
Assuntos
Genoma/genética , Genômica/métodos , Hydra/genética , Animais , Classificação , Regulação da Expressão Gênica , Redes Reguladoras de Genes , Genes , RNA Mensageiro/análiseRESUMO
Although many properties of the innate immune system are shared among multicellular animals, the evolutionary origin remains poorly understood. Here we characterize the innate immune system in Hydra, one of the simplest multicellular animals known. In the complete absence of both protective mechanical barriers and mobile phagocytes, Hydra's epithelium is remarkably well equipped with potent antimicrobial peptides to prevent pathogen infection. Induction of antimicrobial peptide production is mediated by the interaction of a leucine-rich repeats (LRRs) domain containing protein with a TIR-domain containing protein lacking LRRs. Conventional Toll-like receptors (TLRs) are absent in the Hydra genome. Our findings support the hypothesis that the epithelium represents the ancient system of host defence.
Assuntos
Peptídeos Catiônicos Antimicrobianos/genética , Células Epiteliais/imunologia , Hydra/imunologia , Imunidade Inata , Sequência de Aminoácidos , Animais , Peptídeos Catiônicos Antimicrobianos/imunologia , Antioxidantes/farmacologia , Sequência de Bases , Células Epiteliais/microbiologia , Células Epiteliais/ultraestrutura , Evolução Molecular , Flagelina/imunologia , Expressão Gênica/efeitos dos fármacos , Expressão Gênica/imunologia , Hydra/microbiologia , Hydra/ultraestrutura , Microscopia Eletrônica de Transmissão , Dados de Sequência Molecular , Pseudomonas aeruginosa , Receptores de Superfície Celular/efeitos dos fármacos , Receptores de Superfície Celular/imunologia , Receptores de Superfície Celular/metabolismo , Alinhamento de Sequência , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/imunologia , Ácido Úrico/farmacologiaRESUMO
Among the earliest diverging animal phyla are the Cnidaria. Freshwater polyps of the genus Hydra (Cnidaria, Hydrozoa) have long been of general interest because different species of Hydra reveal fundamental principles that underlie development, differentiation, regeneration and also symbiosis. The phylogenetic relationships among the Hydra species most commonly used in current research are not resolved yet. Here we estimate the phylogenetic relations among eight scientifically important members of the genus Hydra with molecular data from two nuclear (18S rDNA, 28S rDNA) and two mitochondrial (16S rRNA, cytochrome oxidase subunit I (COI)) genes. The phylogenetic trees obtained by maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods were generally compatible with present morphological classification patterns. However, the present analysis also bears on several long-standing questions about Hydra systematics and reveals some characteristics of the phylogenetic relationships of this genus that were unknown so far. It indicates that Hydra viridissima, the only species in Hydra, which contains symbiotic algae, might be considered as the sister group to all other species within this genus. Analyses of both nuclear and mitochondrial sequences support the view that Hydra oligactis and Hydra circumcincta are sisters to all other Hydra species. Unexpectedly, we also find that in contrast to its initial description, the strain used for making transgenic Hydra, Hydra vulgaris (strain AEP) is more closely related to Hydra carnea than to other species of Hydra.
Assuntos
Hydra/genética , Filogenia , Animais , Teorema de Bayes , Núcleo Celular/genética , DNA Mitocondrial/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , Hydra/classificação , Hydra/crescimento & desenvolvimento , Funções Verossimilhança , Microscopia de Interferência , Dados de Sequência Molecular , RNA Ribossômico 16S/genética , RNA Ribossômico 18S/genética , RNA Ribossômico 28S/genética , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
Several of the key genes and pathways of vertebrate immunity appear to have much earlier origins than has been assumed previously and are present in some of the simplest of true animals. Surveys of recently released whole-genome sequences and large EST (expressed sequence tag) datasets imply that both the canonical Toll/Toll-like receptor (TLR) pathway and a prototypic complement-effector pathway, involving C3 and several membrane attack complex-perforin proteins, are present in corals and sea anemones, members of the basal phylum Cnidaria. However, both pathways are likely to have degenerated substantially in Hydra, leaving open the molecular mechanism by which antimicrobial activities are induced in this cnidarian. Surprisingly, the cnidarian genomes also encode a protein related to deuterostome RAG1 (recombination activation gene 1). The finding that RAG1 is likely to have originated from a Transib transposase implies that it might be possible to use in silico approaches to identify its target loci in 'lower' animals.