Cardone M F, Ballarati L, Ventura M, Rocchi M, Marozzi A, Ginelli E, Meneveri R
Dipartimento di Anatomia Patologica e Genetica, Sezione di Genetica, Bari, Italy.
Mol Biol Evol. 2004 Sep;21(9):1792-9. doi: 10.1093/molbev/msh190. Epub 2004 Jun 16.
In this article, we report studies on the evolutionary history of beta satellite repeats (BSR) in primates. In the orangutan genome, the bulk of BSR sequences was found organized as very short stretches of approximately 100 to 170 bp, embedded in a 60-kb to 80-kb duplicated DNA segment. The estimated copy number of the duplicon that carries BSR sequences ranges from 70 to 100 per orangutan haploid genome. In both macaque and gibbon, the duplicon mapped to a single chromosomal region at the boundary of the rDNA on the marker chromosome (chromosome 13 and 12, respectively). However, only in the gibbon, the duplicon comprised 100 bp of beta satellite. Thus, the ancestral copy of the duplicon appeared in Old World monkeys ( approximately 25 to approximately 35 MYA), whereas the prototype of beta satellite repeats took place in a gibbon ancestor, after apes/Old World monkeys divergence ( approximately 25 MYA). Subsequently, a burst in spreading of the duplicon that carries the beta satellite was observed in the orangutan, after lesser apes divergence from the great apes-humans lineage ( approximately 18 MYA). The analysis of the orangutan genome also indicated the existence of two variants of the duplication that differ for the length (100 or 170 bp) of beta satellite repeats. The latter organization was probably generated by nonhomologous recombination between two 100-bp repeated regions, and it likely led to the duplication of the single Sau3A site present in the 100-bp variant, which generated the prototype of Sau3A 68-bp beta satellite tandem organization. The two variants of the duplication, although with a different ratios, characterize the hominoid genomes from the orangutan to humans, preferentially involving acrocentric chromosomes. At variance to alpha satellite, which appeared before the divergence of New World and Old World monkeys, the beta satellite evolutionary history began in apes ancestor, where we have first documented a low-copy, nonduplicated BSR sequence. The first step of BSR amplification and spreading occurred, most likely, because the BSR was part of a large duplicon, which underwent a burst dispersal in great apes' ancestor after the lesser apes' branching. Then, after orangutan divergence, BSR acquired the clustered structural organization typical of satellite DNA.
在本文中，我们报告了对灵长类动物中β卫星重复序列（BSR）进化历史的研究。在红毛猩猩基因组中，大部分BSR序列被发现组织成大约100至170 bp的非常短的片段，嵌入在一个60 kb至80 kb的重复DNA片段中。携带BSR序列的复制子的估计拷贝数在每个红毛猩猩单倍体基因组中为70至100个。在猕猴和长臂猿中，该复制子分别映射到标记染色体（分别为13号和12号染色体）上rDNA边界的单个染色体区域。然而，只有在长臂猿中，该复制子包含100 bp的β卫星。因此，该复制子的祖先拷贝出现在旧世界猴中（约25至约35百万年前），而β卫星重复序列的原型发生在猿/旧世界猴分化之后（约25百万年前）的长臂猿祖先中。随后，在小猿与大猿 - 人类谱系分化之后（约18百万年前），在红毛猩猩中观察到携带β卫星的复制子的传播爆发。对红毛猩猩基因组的分析还表明存在两种重复变体，它们在β卫星重复序列的长度（100或170 bp）上有所不同。后一种组织可能是由两个100 bp重复区域之间的非同源重组产生的，并且它可能导致了100 bp变体中存在的单个Sau3A位点的重复，从而产生了Sau3A 68 bpβ卫星串联组织的原型。这两种重复变体，尽管比例不同，但表征了从红毛猩猩到人类的类人猿基因组，优先涉及近端着丝粒染色体。与在新世界猴和旧世界猴分化之前出现的α卫星不同，β卫星的进化历史始于猿的祖先，在那里我们首次记录了一个低拷贝、未重复的BSR序列。BSR扩增和传播的第一步很可能发生，是因为BSR是一个大型复制子的一部分，该复制子在小猿分支后在大猿的祖先中经历了一次爆发性扩散。然后，在红毛猩猩分化之后，BSR获得了卫星DNA典型的簇状结构组织。
