Frisby D P, Weiss R A, Roussel M, Stehelin D
Cell. 1979 Jul;17(3):623-34. doi: 10.1016/0092-8674(79)90270-8.
The chicken is a domesticated form of Red Jungle-fowl (Gallus gallus), which belongs to the Pheasant family (Phasianidae) within the order Galliformes. Domestic chickens carry the genome of the endogenous retrovirus RAV-O as DNA sequences integrated into host chromosomes transmitted through the germ line. We have examined the presence and distribution of RAV-O-related sequences in the DNA of Red Junglefowl and other closely related species of Junglefowl, as well as more distantly related Pheasants and Quail. DNA sequences homologous to RAV-O were analyzed by molecular hybridization in liquid and after electrophoresis of restriction endonuclease fragments. The presence of RAV-O-related sequences in avian DNA does not correlate with phylogenetic relationships. Under stringent conditions of hybridization in liquid, DNA sequences homologous to RAV-O cDNA were detected at high levels (greater than 80% homology( only in the genomes of the domestic chicken and its phylogenetic ancestor, the Red Junglefowl (Gallus gallus). The DNA of two other species of Gallus (G. sonnerati, Sonnerat's Junglefowl and G. varius, Green Junglefowl), of Ring-necked Pheasant and of Japanese Quail contained sequences with less than 10% homology to RAV-O cDNA. Under conditions permitting mismatching, however, Ring-necked Pheasant DNA hybridized up to 50% of the RAV-O cDNA, and Quail DNA 24%, whereas the extent of hybridization to Sonnerat's and Green Junglefowl DNA was not markedly increased. Analysis of restriction enzyme digests revealed several distinct fragments of DNA hybridizing to chick retrovirus cDNA in both Red Junglefowl and domestic chicken, and multiple fragments in DNA from two species of Phasianus. No fragments with sequences related to chicken retroviruses were found, however, in digests of DNA prepared from Sonnerat's, Ceylonese and Green Junglefowl, from two other Pheasant genera (Chrysolophus and Lophura), or from one Quail genus (Coturnix). Thus the DNA of three Junglefowl species closely related to Gallus gallus lacked RAV-O sequences while the DNA of more distantly related Phasianus species showed significant homology. These results show that RAV-O-related sequences have not diverged together with the normal host genes during the evolution of the Phasianidae. Although RAV-O sequences are endogenous in all domestic chickens and Red Junglefowl studied thus far, it appears that the RAV-O genome has been introduced relatively recently into the germ line of Gallus gallus, following speciation but before domestication, and independently of the related sequences found in members of the genus Phasianus.
鸡是红原鸡（原鸡）的驯化品种，原鸡属于鸡形目雉科。家鸡携带内源性逆转录病毒RAV - O的基因组，其DNA序列整合到通过种系传递的宿主染色体中。我们研究了红原鸡以及其他亲缘关系较近的原鸡品种、亲缘关系较远的雉鸡和鹌鹑的DNA中RAV - O相关序列的存在情况和分布。通过液相分子杂交以及对限制性内切酶片段进行电泳后，对与RAV - O同源的DNA序列进行了分析。禽类DNA中RAV - O相关序列的存在与系统发育关系无关。在液相杂交的严格条件下，仅在家鸡及其系统发育祖先红原鸡（原鸡）的基因组中，检测到与RAV - O cDNA同源的DNA序列，且同源性较高（大于80%）。另外两种原鸡（索氏原鸡和绿原鸡）、环颈雉和日本鹌鹑的DNA中，与RAV - O cDNA的同源序列不到10%。然而，在允许错配的条件下，环颈雉DNA与RAV - O cDNA的杂交率高达50%，鹌鹑DNA为24%，而与索氏原鸡和绿原鸡DNA的杂交程度没有明显增加。对限制性酶切片段的分析表明，在红原鸡和家鸡中，均有几个不同的DNA片段与鸡逆转录病毒cDNA杂交，在两种雉属鸟类的DNA中有多个片段杂交。然而，在从索氏原鸡、锡兰原鸡和绿原鸡、另外两个雉属（锦鸡属和凤冠雉属）或一个鹌鹑属（鹌鹑属）制备的DNA酶切产物中，未发现与鸡逆转录病毒相关序列的片段。因此，与原鸡亲缘关系密切的三种原鸡品种的DNA中缺乏RAV - O序列，而亲缘关系较远的雉属鸟类的DNA则显示出显著的同源性。这些结果表明，在雉科动物的进化过程中，RAV - O相关序列并未与正常宿主基因一起分化。尽管到目前为止，在所有研究的家鸡和红原鸡中RAV - O序列都是内源性的，但似乎RAV - O基因组是在物种形成之后、驯化之前相对较近的时期引入原鸡的种系中的，并且与雉属成员中发现的相关序列无关。
