Genomic Imprinting in Viviparous Fishes

胎生鱼类的基因组印记

• 批准号: 0110930
• 负责人: Michael O'Neill
• 金额: $ 34.5万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0110930&HistoricalAwards=false
• 关键词: Genomic; Imprinting; Viviparous; Fishes

Higher organisms contain two copies, or alleles, of every gene, one inherited maternally and the other inherited paternally, and for most genes both copies are expressed. Having two copies of every gene, known as diploidy, is thought to protect organisms from the deleterious effects of recessive mutations. For imprinted genes, however, only one copy is expressed. Which copy of an imprinted gene pair is to be expressed is determined by which parent it was inherited from. In other words, some genes are expressed only when inherited maternally and some only when inherited paternally. About forty genes have been identified in mice, humans and other mammals that show imprinted patterns of expression, and there is evidence to suggest that there may be 200 or more imprinted genes in the mammalian genome. Because silencing of one allele of a gene pair abolishes the protection against recessive mutation, it is difficult to explain why such a system of gene expression exists and how it evolved. Of several evolutionary theories proposed to explain genomic imprinting, only one, the conflict model, has been broadly supported by molecular genetic, population genetic and embryological evidence. The conflict model posits that genomic imprinting is the outcome of a conflict between parents over their relative contributions to developing offspring. In mammals, the mother is the sole source of nutrients to gestating young. In polygamous breeding animals, the genes transmitted by fathers will evolve mechanisms, or imprints, to take advantage of the mothers exclusive resource input to his genetic offspring. This puts the mothers genes at a disadvantage since focussing resources on the offspring of one father compromises her output to the offspring of her other mates and may reduce her reproductive output altogether. Maternally transmitted genes have, therefore, evolved mechanisms to counteract the imprinted genes transmitted paternally. The conflict model predicts the general rule that growth-enhancing genes are paternally active and maternally silent, and that growth-suppressing genes are maternally active and paternally silent. This type of imprinted gene expression is peculiar to mammals, which are all viviparous, and in all of which developing embryos are supported by a placental connection with the mother. An essential test of the conflict model is to search for imprinted genes in animals that have evolved viviparity and placentation independent of mammals. This project investigates whether a genus of viviparous fish, Poeciliopsis, has evolved genomic imprinting in the context of parental conflict. This work promises not only to test the evolutionary model, but also to provide a greater insight into the molecular mechanisms underlying imprinted gene expression and the function of imprinting in embryonic development.

高等生物的每一个基因都有两个拷贝或等位基因，一个是母系遗传的，另一个是父系遗传的，大多数基因的两个拷贝都有表达。每个基因都有两个拷贝，被称为二倍体，被认为可以保护生物体免受隐性突变的有害影响。 然而，对于印记基因，只有一个拷贝被表达。 一对印记基因的哪一个拷贝将被表达取决于它是从哪一个亲本遗传的。 换句话说，有些基因只有在母系遗传时才表达，有些只有在父系遗传时才表达。 在小鼠、人类和其他哺乳动物中已经鉴定出大约40个基因，它们显示出印记表达模式，有证据表明哺乳动物基因组中可能有200个或更多的印记基因。 由于基因对中一个等位基因的沉默会破坏对隐性突变的保护，因此很难解释为什么这样一个基因表达系统存在以及它是如何进化的。 在解释基因组印记的几种进化理论中，只有冲突模型得到了分子遗传学、群体遗传学和胚胎学证据的广泛支持。 冲突模型假定基因组印记是父母之间关于他们对后代发育的相对贡献的冲突的结果。 在哺乳动物中，母亲是孕育幼崽的唯一营养来源。 在一夫多妻的繁殖动物中，由父亲传递的基因将进化出机制或印记，以利用母亲对他的遗传后代的独家资源输入。 这使得母亲的基因处于不利地位，因为将资源集中在一个父亲的后代上会损害她对其他配偶后代的输出，并可能完全减少她的生殖输出。 因此，母系传递的基因进化出了抵消父系传递的印记基因的机制。冲突模型预测了一般规则，即生长促进基因是父系活跃和母系沉默，而生长抑制基因是母系活跃和父系沉默。 这种类型的印记基因表达是哺乳动物所特有的，它们都是胎生的，并且在所有这些哺乳动物中，发育中的胚胎都由与母亲的胎盘连接支持。 冲突模型的一个重要测试是在独立于哺乳动物进化出胎生和胎盘的动物中寻找印记基因。 本研究旨在探讨一种胎生鱼类--拟花鱼在双亲冲突的背景下是否进化出了基因组印记。 这项工作不仅有望测试进化模型，而且还提供了一个更深入的了解印迹基因表达的分子机制和胚胎发育中的印迹功能。