發(fā)布時(shí)間：2018-07-07 14:13

  本文選題：鯨類 + 味覺基因�。� 參考：《南京師范大學(xué)》2016年博士論文

【摘要】：人類可以感知5種基本的味覺,即酸、甜、苦、咸和鮮,這5種味覺在哺乳動(dòng)物的生理和生態(tài)適應(yīng)過程中發(fā)揮重要作用。在陸生哺乳動(dòng)物中,這些味覺受體基因的分子遺傳學(xué)研究已經(jīng)較為廣泛,然而在海洋哺乳動(dòng)物中相應(yīng)的研究卻較為稀缺。本研究在代表性的鯨類物種中調(diào)查了5種味覺感知相關(guān)的受體基因。通過對(duì)這些味覺受體基因的序列比對(duì),我們?cè)诰幋a酸、甜、鮮和苦味的受體基因上檢測(cè)到了移碼和／或提前終止密碼子突變,通過把第一位提前終止密碼子標(biāo)注到假基因的蛋白二級(jí)結(jié)構(gòu)上,我們發(fā)現(xiàn)這些突變均導(dǎo)致了蛋白二級(jí)結(jié)構(gòu)的縮短,從而導(dǎo)致其喪失了原有的功能。進(jìn)一步的選擇壓力分析表明編碼酸、甜和鮮味的受體基因上的選擇壓力并未完全放松,提示它們的假基因化可能是近期事件,而苦味受體所受到的選擇壓力幾乎完全放松,表明它們的假基因化可能發(fā)生的較早。編碼咸味受體的3個(gè)基因在鯨類中仍然是完整的,我們推測(cè)這可能和咸味受體在腎臟、肺、皮膚等處的鈉離子吸收功能相關(guān),至于鯨類是否保留有咸味感知能力仍有待于進(jìn)一步研究。為了進(jìn)一步了解鯨類對(duì)全水生環(huán)境的適應(yīng),我們利用已發(fā)表的鯨類基因組(白淍豚和小須鯨)并重測(cè)了3個(gè)瓶鼻海豚進(jìn)行了種間和種內(nèi)的比較基因組學(xué)分析。基于白淍豚、小須鯨、牛、狗、人和小鼠的單拷貝直系同源基因,我們利用PAML正選擇分析揭示了在鯨類起源及其隨后的分化過程中,它們的先天性免疫系統(tǒng)出現(xiàn)了普遍的適應(yīng)性進(jìn)化。正選擇分析還進(jìn)一步揭示了和脂肪酸轉(zhuǎn)運(yùn)、活化以及三酰甘油合成相關(guān)的基因在白淍豚和小須鯨中均是受到正選擇的,這和它們擁有厚厚的鯨脂也是一致的。此外,涉及到滲透調(diào)節(jié)、骨密度調(diào)控和低氧耐受的基因在鯨類中也是受到正選擇的,這和它們需要應(yīng)對(duì)截然不同的滲透壓、快速游泳和潛水等行為是息息相關(guān)的。為了進(jìn)一步挖掘鯨類對(duì)咸淡水的適應(yīng),我們利用海洋鯨類(小須鯨和瓶鼻海豚)和淡水鯨類(白淍豚)的重測(cè)序數(shù)據(jù)篩選單核苷酸多態(tài)性位點(diǎn),并用PROVEAN軟件評(píng)估這些氨基酸替換對(duì)蛋白功能的影響。PROVEAN分析進(jìn)一步揭示了咸水和淡水鯨類中擁有種間核苷酸差異的基因涉及到嗅覺和視覺系統(tǒng)、DNA損傷修復(fù)和色素沉著等�；贛SMC的種群動(dòng)態(tài)分析也表明白淍豚的功能性滅絕可能是棲息地的破壞和極端的人類活動(dòng)造成的,這與之前的白淍豚基因組分析結(jié)果也是一致的。
[Abstract]:Humans can perceive five basic taste senses, namely, sour, sweet, bitter, salty and fresh, which play an important role in the physiological and ecological adaptation of mammals. In terrestrial mammals, the molecular genetics of these taste receptor genes has been widely studied, but the corresponding research in marine mammals is relatively scarce. This study investigated five receptor genes associated with taste perception in a typical cetacean species. By sequencing these taste receptor genes, we detected frameshift and / or early termination codon mutations in receptor genes that encode acid, sweet, fresh and bitter. By tagging the first early termination codon to the protein secondary structure of the pseudogenic gene, we found that these mutations all led to the shortening of the protein secondary structure, which resulted in the loss of its original function. Further selection stress analysis showed that the selection pressure on the genes encoding acid, sweet and delicious receptors was not completely relaxed, suggesting that their pseudogenization might be a recent event, while the selection pressure on bitter receptors was almost completely relaxed. This suggests that their pseudogenization may have occurred earlier. The three genes that encode salty receptors are still intact in whales, and we speculate that this may be related to sodium absorption in the kidneys, lungs, skin, etc. Whether cetaceans retain saltwater perception remains to be further studied. In order to further understand the adaptation of cetaceans to the whole aquatic environment, we used the published cetacean genomes (white porpoises and minke whales) to re-measure the comparative genomics analysis of three flask dolphins in both species and species. Based on the single-copy lineal homologous genes of white porpoises, minke whales, cattle, dogs, humans and mice, we used PAML positive selection analysis to reveal the origin and subsequent differentiation of cetaceans. Their innate immune system has developed a general adaptive evolution. The positive selection analysis further revealed that genes associated with fatty acid transport, activation and triglyceride synthesis were both positively selected in both white porpoises and minke whales, which were consistent with their possession of thick blubber whales. In addition, genes involved in osmotic regulation, bone mineral density regulation and hypoxia tolerance are also being selected in whales, which is closely related to their response to radically different osmotic pressures, rapid swimming and diving. To further explore the adaptation of whales to brackish water, we used resequencing data from marine whales (minke whales and flask dolphins) and freshwater whales (white porpoises) to screen single nucleotide polymorphisms. The effect of these amino acid substitutions on protein function was evaluated by PROVEAN software. The results further revealed that genes with interspecific nucleotide differences in brackish water and freshwater whales were involved in DNA damage repair and pigmentation of olfactory and visual systems. The population dynamics analysis based on MSMC also showed that the functional extinction may be caused by habitat destruction and extreme human activities, which is consistent with the previous results of genome analysis.
【學(xué)位授予單位】：南京師范大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：Q953
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本文編號(hào)：2105215