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Changes in gene expression during sex chromosome evolution in the dioecious plant Silene latifolia

雌雄异株植物Silene latifolia性染色体进化过程中基因表达的变化

基本信息

批准号：
BB/E020909/1
负责人：
Deborah Charlesworth
金额：
$ 43.62万
依托单位：
University of Edinburgh
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=BB%2FE020909%2F1
关键词：
Changes gene expression during sex

项目摘要

We propose studies of expression levels of genes on the sex chromosomes of the plant Silene latifolia. This plant is one of the minority of plant species that is not hermaphroditic, but has separate sexed individuals, and an X/Y sex chromosomal sex-determination system like that in mammals, including humans. It is well known that the Y (male-determining) chromosomes evolved from an ancestral chromosome that was similar to other chromosomes, and the X chromosomes in female mammals are still not very different from other chromosomes, though they have some distinctive features that probably reflect their evolution as sex chromosomes. The Y chromosomes, however, are extremely strange in both mammals and in the other very well studied system, the fruitfly, Drosophila. In both cases, the Y chromosomes carry only very few genes, and only a small proportion of them are present on the X (in Drosophila melanogaster, no genes appear to be shared between the X and Y chromosomes, and in mammals there is a handful of such genes); in both cases the Y has acquired genes not present on the X. How these strange genetic properties evolved is an interesting question. Theories for the process of 'genetic erosion' (or 'degeneration') of Y chromosomes from an initial state in which most loci were shared with the X chromosome, suggest that genes on Y chromosomes lose their former functions and can then be deleted, and that this occurs because the X and Y chromosomes do not cross-over and undergo genetic recombination like other chromosomes. Population genetic models of regions of genome without genetic recombination predict that advantageous genes are less likely to be able to spread, and that natural selection will be unable to resist spread of disadvantageous genes. To study this genetic degeneration process, we need genes that are located on the sex chromosomes of a species in which degeneration is occurring. Because mammalian and fruitfly sex chromosomes evolved long ago, their Y have already lost most genes present on the X, so they are not well suited for such studies. Some plant species are known to have evolved sex chromosomes much more recently than these animals, and these are of interest for studying Y chromosome genetic erosion. We propose to work on the sex chromosomes of the plant Silene latifolia, the white campion. Its sex chromosomes have been studied cytologically since the early days of genetics, and in recent years a few genes on the sex chromosomes have been sequenced. Our project is to test in a direct manner for genetic degeneration by testing whether Y chromosomal copies of several genes are expressed at lower levels than X-linked copies of the same genes. This is now possible because we have developed a straightforward approach to identifying sex-linked genes (allowing us to discover some new genes on the sex chromosomes); thus there are now enough loci to gain a general picture of whether Y copies have low expression levels, and more genes on the sex chromosomes can readily be found. The project includes tests to show whether any differences found are due to low Y expression , versus the less likely, but also interesting, possibility of an increase in expression of X copies since the species separated from its hermaphrodite relative, the bladder campion, S. vulgaris. The expression experiments are possible because the X and Y copies are similar enough that short sequences of both can be amplified simultaneously in experiments, yet their sequences differ enough that expression of each of the two different alleles can be measured.

我们建议研究植物 Silene latifolia 性染色体上基因的表达水平。这种植物是少数非雌雄同体的植物物种之一，但具有独立的性别个体，以及类似于哺乳动物（包括人类）的 X/Y 性染色体性别决定系统。众所周知，Y（决定男性）染色体是从与其他染色体相似的祖先染色体进化而来的，而雌性哺乳动物的X染色体仍然与其他染色体没有太大区别，尽管它们具有一些独特的特征，可能反映了它们作为性染色体的进化。然而，在哺乳动物和另一个经过充分研究的系统——果蝇——果蝇中，Y 染色体都极其奇怪。在这两种情况下，Y 染色体只携带很少的基因，并且只有一小部分基因存在于 X 上（在果蝇中，X 和 Y 染色体之间似乎没有共享基因，而在哺乳动物中则有少数这样的基因）；在这两种情况下，Y 都获得了 X 上不存在的基因。这些奇怪的遗传特性如何进化是一个有趣的问题。 Y 染色体从大多数基因座与 X 染色体共享的初始状态开始“遗传侵蚀”（或“退化”）过程的理论表明，Y 染色体上的基因失去了以前的功能，然后可以被删除，而发生这种情况是因为 X 和 Y 染色体不像其他染色体那样交叉和经历遗传重组。没有基因重组的基因组区域的群体遗传模型预测，有利基因不太可能传播，而自然选择将无法抵抗不利基因的传播。为了研究这种遗传退化过程，我们需要位于正在发生退化的物种的性染色体上的基因。由于哺乳动物和果蝇性染色体很久以前就进化了，它们的 Y 染色体已经丢失了 X 染色体上的大部分基因，因此它们不太适合此类研究。已知一些植物物种比这些动物更晚进化出性染色体，这些对于研究 Y 染色体遗传侵蚀很有意义。我们建议研究白坎皮植物 Silene latifolia 的性染色体。自遗传学早期以来，人们就对其性染色体进行了细胞学研究，近年来，性染色体上的一些基因已被测序。我们的项目是通过测试多个基因的 Y 染色体拷贝的表达水平是否低于相同基因的 X 连锁拷贝的表达水平，以直接方式测试遗传退化。现在这是可能的，因为我们已经开发出一种直接的方法来识别与性别有关的基因（使我们能够在性染色体上发现一些新基因）；因此，现在有足够的基因座来大致了解 Y 拷贝是否具有低表达水平，并且可以很容易地发现性染色体上的更多基因。该项目包括一些测试，以显示所发现的任何差异是否是由于 Y 表达低所致，而自该物种与其雌雄同体亲戚、膀胱坎皮恩 (S. vulgaris) 分离以来，X 拷贝表达增加的可能性较小，但也很有趣。表达实验是可能的，因为 X 和 Y 拷贝足够相似，可以在实验中同时扩增两者的短序列，但它们的序列差异足够大，可以测量两个不同等位基因中每一个的表达。