Bachmann-Waldmann Christa, Jentsch Stephan, Tobler Heinz, Müller Fritz
Departement of Biology, Zoology, University of Fribourg, Chemin du Musée 10, Fribourg CH-1700, Switzerland.
Mol Biochem Parasitol. 2004 Mar;134(1):53-64. doi: 10.1016/j.molbiopara.2003.11.001.
Chromatin diminution in the parasitic nematodes Ascaris suum and Parascaris univalens represents a rather complex molecular phenomenon that includes chromosomal breakage, DNA degradation and new telomere formation. At a given elimination site, DNA breakage and new telomere addition does not take place at a single chromosomal locus but at many different places within a several kilobase long chromosomal region, referred to as chromosomal breakage region (CBR). Here we describe the cloning and the characterisation of seven CBRs from A. suum and P. univalens and we show that the process has been conserved between the two species. A detailed sequence comparison provides evidence that the sequences of the CBRs and their flanking regions are not directly important for the specification of the elimination sites. Six out of the seven CBRs are conserved between the two nematode species, suggesting that they have already existed in a common ancestor. We present a hypothesis stating that the elimination process ensures the maintenance of a functional somatic genome and concomitantly allows extremely rapid and profound changes in the germ line genome, thereby allowing the development of new germ line specific functions and thus providing a selective advantage for the chromatin eliminating nematodes during further evolution.
寄生线虫猪蛔虫和单宫副蛔虫中的染色质消减是一种相当复杂的分子现象，包括染色体断裂、DNA降解和新端粒形成。在给定的消除位点，DNA断裂和新端粒添加并非发生在单个染色体位点，而是发生在一个几千碱基长的染色体区域内的许多不同位置，该区域称为染色体断裂区域（CBR）。在这里，我们描述了来自猪蛔虫和单宫副蛔虫的七个CBR的克隆和特征，并且我们表明这一过程在两个物种之间是保守的。详细的序列比较提供了证据，表明CBR及其侧翼区域的序列对于消除位点的特异性并非直接重要。七个CBR中有六个在这两种线虫物种之间是保守的，这表明它们在共同祖先中就已经存在。我们提出一个假说，即消减过程确保了功能性体细胞基因组的维持，同时允许生殖系基因组发生极其快速和深刻的变化，从而允许新的生殖系特异性功能的发展，进而为染色质消减线虫在进一步进化过程中提供选择优势。
