Do epigenomic factors influence twin bulls performances?

随着基因组评估工具的发展，现在有可能估计出生时的繁育价值。为了提高遗传改良率，最近有一种趋势是尽快使用幼年动物，为了增加其高优点遗传背景的传播率，胚胎分裂正越来越多地被使用。双胞胎拥有相同的DNA组成，在所有逻辑上，他们在基因评估方面的表现即使不是完全相同，也应该是相似的。事实上，最近的数据表明，双胞胎之间可能会出现育种值的差异。这些差异可能与评价本身有关，也可能来自其他来源。在分子水平上，表型是基因活性的结果，已经证明表观基因组可以很大程度上影响基因的表达。根据定义，表观基因组代表所有引起DNA构象变化并将影响基因表达的可逆修饰。表观基因组修饰的一个很好的例子是DNA甲基化，它通过关闭与细胞类型无关或危险的基因来驱动细胞特有的基因表达。到目前为止，很少有人注意表观基因组的影响，因为它被认为是暂时的。然而，表观遗传标记至少可以通过两代，这一点现在已经被广泛接受。本项目的目的是确定双胞胎公牛的精子是否具有相似、相同或不同的DNA甲基化标记。这些初步结果对乳制品生产商很重要，因为通过适应子宫环境或出生后条件来操纵这些潜在差异的来源，可能会影响精英动物的生产方式。

With the development of tools for genomic evaluation, it is now possible to estimate breeding values at birth. To increase the rate of genetic improvement, there is a recent trend to use young animals as soon as possible and, in order to increase the rate of dissemination of their high merit genetic background, embryo splitting is becoming increasingly used. Twins share an identical DNA makeup and should, in all logic, lead to similar if not identical performances in regards to their genetic evaluations. In fact, recent data have shown that differences in breeding values can arise between twins. These differences may pertain to the evaluation itself or may arise from other sources. At the molecular level, phenotypes are the resulting from gene activity and it has been shown that the epigenome can largely influence gene expression. By definition, the epigenome represents all reversible modifications that induce changes in the DNA conformation and that will influence gene expression. A good example of an epigenomic modification is DNA methylation, which drives cell specific gene expression by shutting down genes that are irrelevant or dangerous to a cell type. So far, very little attention was given to the impact of the epigenome as it was deemed to be transient. However, it is now well accepted that epigenetic marks can be carried through at least 2 generations. The objective of the present project is to determine whether the sperm of twin bulls harbour similar, identical or divergent DNA methylation marks. These initial results are of importance to dairy producers because manipulating the source of these potential divergences, through adaptation of the uterine environment or post natal conditions, could influence how elite animals are produced.