RESUMO
BACKGROUND: We describe the genome of the western painted turtle, Chrysemys picta bellii, one of the most widespread, abundant, and well-studied turtles. We place the genome into a comparative evolutionary context, and focus on genomic features associated with tooth loss, immune function, longevity, sex differentiation and determination, and the species' physiological capacities to withstand extreme anoxia and tissue freezing. RESULTS: Our phylogenetic analyses confirm that turtles are the sister group to living archosaurs, and demonstrate an extraordinarily slow rate of sequence evolution in the painted turtle. The ability of the painted turtle to withstand complete anoxia and partial freezing appears to be associated with common vertebrate gene networks, and we identify candidate genes for future functional analyses. Tooth loss shares a common pattern of pseudogenization and degradation of tooth-specific genes with birds, although the rate of accumulation of mutations is much slower in the painted turtle. Genes associated with sex differentiation generally reflect phylogeny rather than convergence in sex determination functionality. Among gene families that demonstrate exceptional expansions or show signatures of strong natural selection, immune function and musculoskeletal patterning genes are consistently over-represented. CONCLUSIONS: Our comparative genomic analyses indicate that common vertebrate regulatory networks, some of which have analogs in human diseases, are often involved in the western painted turtle's extraordinary physiological capacities. As these regulatory pathways are analyzed at the functional level, the painted turtle may offer important insights into the management of a number of human health disorders.
Assuntos
Adaptação Fisiológica/genética , Genoma/genética , Modelos Genéticos , Filogenia , Tartarugas/genética , Animais , Composição de Bases/genética , Evolução Molecular , Feminino , Congelamento , Humanos , Hipóxia/genética , Hipóxia/fisiopatologia , Sistema Imunitário/metabolismo , Isocoros/genética , Funções Verossimilhança , Longevidade/genética , Masculino , MicroRNAs/genética , MicroRNAs/metabolismo , Anotação de Sequência Molecular , Família Multigênica , Pseudogenes/genética , Padrões de Referência , Sequências Repetitivas de Ácido Nucleico/genética , Seleção Genética , Processos de Determinação Sexual , TemperaturaRESUMO
Within the rhabditid phylogeny of nematodes, the great majority of species are gonochoristic, having evolved as obligate male/female species. In contrast, the well-studied nematode model system, Caenorhabditis elegans, is androdioecious, utilizing a hermaphroditic/male reproductive system. We have previously determined that in the arrested oocytes of old-aged C. elegans hermaphrodites with depleted sperm, large cytoplasmic ribonucleoprotein foci form. The formation of these foci is reversible, as they dissociate within 3 h after a male mates with the hermaphrodite, resupplying it with sperm. The functional significance of these oocyte foci is not known and previously has not been clear for a hermaphroditic species in which oocytes of young adults wait only approximately 23 min to be fertilized. One hypothesis is that the foci function to maintain maternal mRNAs in oocytes while fertilization is delayed. In this paper, we examine four gonochoristic rhabditid species: Caenorhabditis remanei, Caenorhabditis sp. CB5161, Caenorhabditis sp. PS1010, and Rhabditella axei DF5006. We demonstrate that in three of these four species, ovulation arrests in unmated females until mating occurs and large cytoplasmic foci develop in arrested oocytes. The oocyte foci contain nuclear pore proteins and, in C. remanei at least, the RNA-binding protein MEX-3 as well as RNA. We speculate that these foci maintain the integrity of ooctyes, possibly maintaining the stability or translational repression of maternal mRNAs in unmated females. We further speculate that their presence in oocytes of old-aged C. elegans hermaphrodites is due to conservation from an ancestral gonochoristic state.
