| 其他摘要 | Growth hormone (GH) along with prolactin, placental lactogen and related proteins in mammals formed the GH/PRL gene superfamily, which possesses similar gene structure and function. In most of mammals, both prolactin and growth hormone are single copied genes. While, in primate, a cluster of genes originated from tandem gene duplication of GH were observed. By contraries, in rodent, GH is a single copied gene, while PRL and other related genes formed a gene family. By PCR, cloning and sequencing, we obtained totally 35 growth hormone (GH)4ike genes from seven primate species. Phylogenetic analysis strongly suggests monophyly for new world monkeys (NWM) GH-like genes with respect to those of old world monkeys (OWM)/hominoids, which indicates independent gene duplications have occurred in OWM/Hominoids and NWM GH-like genes. Our analysis demonstrates that multiple gene duplications and several gene conversion events have occurred during the evolution of GH gene family. We also revealed that different family members evolved at different rates and under different selective constraints. GHN genes in both hominoids and 0WM evolved under strong purifying selection. In contrast, CSH genes in both lineages are probably evolved under near neutral selection. GHV genes in OWM and hominoids evolved at different evolutionary rates and underwent different selective constraints. There are three main clusters of genes in putatively functional NWM GH-like genes based on our gene tree. Interestingly, these three clusters of genes evolved under purifying selection, near neutral selection and positive selection individually. Detailed analysis showed that the evolutionary pattern of this gene family in primate is in agreement with the so-called birth-and-death process, which characterized by frequently gene duplication and pseudogenization. Prolactin gene family in rodent consists of multiple members; they coordinate in the process of reproduction and pregnancy. In this study, we identified two novel members of this gene family in rat by blast the published genome database. Combing evidence from phylogenetic analysis, gene conversion test and the relative chromosome location comparison, we believe that independent gene duplications have occurred in PL-1 and PL-II subfamilies after the divergence of mouse and rat. The evolution of PRL gene family is very complex somewhat because it contains not only the original 5-exon members, but also those 6-exon members, who acquired one extra exon in-between exon 2 and exon 3 of the prototypical 5 exon structure. Unexpectedly, we observed that the origins of this extra exon in two groups are independent In group A genes, it originated by an external fragment insertion, while in group B" it originated by a previous noncoding region. Further analysis suggests relaxation of purifying selection as major forces during evolution of these genes. Hormones need to bind to their receptor to transduce the signal and then to fulfill their biological functions. Thus analysis about coevolution between ligands and their receptor is very important. In this paper we show a clear case of coevolution between prolactin (PRL) gene and its receptor (prolactin receptor, PRLR) in mammals. First we observed episodic evolution of the extracellular domain and the intracellular domain of the PRLR, which is closely consistent with that seen in PRL. Correlated evolutions were demonstrated both between PRL and its receptor and between the two domains of the PRLR using Pearson's correlation coefficient. Besides, as have seen in growth hormone, prolactin gene shows an episodic evolutionary pattern in primate, and the episode of fast evolution was due to relaxation of purifying selection. |
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