| 其他摘要 | The mammalian motilin/ghrelin-associated gene family encodes three gastrointestinal hormones, motilin, ghrelin and obestatin. Each of these three functionally distinct peptide hormones has a unique, but related, receptor MLNR, GHSR and GPR39 respectively. To determine whether the evolutionary history of receptors parallels that of their cognate ligands and gain a better understanding of how novel interactions and physiological functions evolve after gene duplication, we conducted phylogenetic analyses and molecular inferences. Here we show that, MLN and GHRL descended from a common ancestor, and that gene duplication occurred shortly after the divergence of amphibians and amniotes, after the origin of two additional endoproteinase recognition sites（which can give rise to a new posttranslational processed peptide, e.g. obestatin in mammalian GHRL）. The evolutionary history of the receptors differs from their cognate legends. GPR39 diverged first, and an ancestral GHSR–like receptor gave rise to a fish specific cluster A, GHSR and MLNR by tandem gene duplication that occurred before the divergence of tetrapods and fish. The Ghrelin/GHSR system has been maintained and functionally conserved from fish to mammals, while motilin–MLNR specificity only evolved, as the result of hormone–receptor coevolution, after the hormone gene duplication. A model for the evolution of novelties in tightly integrated biological systems is proposed under which a period of gene sharing ordinarily precedes the evolution of distinct functionality. Novel interactions emerge when a newly generated molecule is recruited as a binding partner of an old molecule, which was previously constrained by selection for different function. Gene duplication then allows each daughter gene to specialize for subfunctions of the ancestral gene. Moreover, we did molecular authentication of newly discovered live Cuora yunnanensis individuals and use molecular data evaluated the evolutionary distinctiveness of C. yunnanensis. Cuora yunnanensis, the Yunnan box turtle, has been regarded as extinct, known only from 12 specimens collected from Yunnan, China, before 1908. And it has drawn much attention in conservative biology research. We sequenced 1725 base pairs of mitochondrial DNA from three newly discovered live C. yunnanensis individuals, and present a molecular phylogenetic analysis of the genus Cuora with complete taxon sampling, including the former sequences of an old museum C. yunnanensis specimen（MNHN 1907.10）. Our phylogenetic analysis implies that in accordance with morphological authentication the newly discovered individuals are genuine C. yunnanensis, as well as corroborated the sequences of that old museum specimen. C. yunnanensis is not of recent hybrid origin, but rather represents a distinct evolutionary lineage with more or less within species genetic diversity. This work is a good example that molecular phylogeny provide important information in endangered animal conservation. Our results prompt strong evidence that C. yunnanensis is still existed somewhere in earth, but highly threatened situation of this species has not changed. Intense scientific fieldwork is required to locate and subsequently protect the populations that may have survived as well as their natural habitats. |
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