Study On The Adaptation, Eyolution And Variation Of The P53Gene From Qinghai-Tibetan Mammals

As a transcription factor, p53induces cell cycle arrest and apoptosis under stresses through a series of target genes to maintain the genome integrity and determine the cell fate. Myospalax baileyi (Thomas,1911) and Microtus oeconomus (Pallas,1776) inhabit the meadow at3300m altitude on the Qinghai-Tibetan plateau. The former lives in the degenerative alpine meadow and the latter lives in the shrub meadow of Potentilla fruticosa. Both of them are dominant species of Qinghai-Tibetan Plateau. The Myospalax baileyi spends its whole life cycle in burrows underground. The Microtus oeconomus leads a semi-underground life. They bear a hypoxic and cold environment.The mutation of the p53genes from Myospalax baileyi and Microtus oeconomus was analyzed by cloning and sequencing the p53gene. Their p53genes have analogies with that of human, rat and mouse to different degrees. The codon104,127,215in the core domain and322in the C-terminus of Myospalax baileyi p53and the codon86in the N-terminus,104,258in the core domain and340in the C-terminus of Microtus oeconomus p53mutated.Investigating the transcriptional regulation of Myospalax and Microtus p53towards target genes showed that the Myospalax p53has a significantly higher transactivationg towards the pro-apoptotic targets IGFBP3and Apafl; the Microtus p53, however, has a much lower transactivation towards these two target genes. Both Myospalax and Microtus p53has a similar ability to transactivate p21(involved in cell cycle arrest) and Hdm2(involved in p53homeostasis) with that of human p53. Mutagenesis experiments demonstrated that the mutation of the codon104from Ser to Asn of the Myospalax p53is related with its strong transactivation towards the pro-apoptotic target genes. The mutation of the codon104from Ser to Glu of the Microtus p53is critical for its weak transactivation towards the pro-apoptotic target genes.Study on the influence of Myospalax and Microtus p53on cell fate showed that, the Microtus p53has a significantly weaker capability to induce apoptosis. Humanization of the codon104increased the pro-apoptotic ability, suggesting that the weaker pro-apoptotic ability of Microtus p53is due to the mutation S104E. This may be the strategy of Microtus to adapt to the hypoxic habitat by preventing the hypoxia-induced apoptosis. The Myospalax p53has a similar capability to induce apoptosis with that of human p53. Although the Myospalax p53has stronger transactivation towards the pro-apoptotic target gene IGFBP3and Apafl, it lost the transrepression towards the antiapoptotic gene Bcl-2, and even induced a transactivation of Bcl-2. The antiapoptotic and pro-apoptotic ability form a balance.Our study also demonstrated that, the capability of p53transactivation towards IGFBP3decreased while Bcl-2increased under acidic environment, suggesting that, under hypoxia/high CO2environment, the balance of antiapoptotic and pro-apoptotic ability prefers the antiapoptotic ability. This may serves as a strategy for Myospalax adaptation to hypoxia/high CO2environment.The present study used molecular cloning strategies to demonstrate the mutated sites of Myospalax and Microtus p53. These mutants showed reverse transcriptional patterns towards pro-apoptotic target genes, with different pro-apoptotic capabilities. The results reflected the diversity of transcriptional mechanisms adapting to hypoxia enviorment. The mutations may be the molecular mechanisms of adaptation to the plateau environment during evolution.