Institute of Molecular and Cellular Biology SВ RAS, Novosibirsk, Russia.
BMC Biol. 2013 Aug 6;11:90. doi: 10.1186/1741-7007-11-90.
Most eukaryotic species represent stable karyotypes with a particular diploid number. B chromosomes are additional to standard karyotypes and may vary in size, number and morphology even between cells of the same individual. For many years it was generally believed that B chromosomes found in some plant, animal and fungi species lacked active genes. Recently, molecular cytogenetic studies showed the presence of additional copies of protein-coding genes on B chromosomes. However, the transcriptional activity of these genes remained elusive. We studied karyotypes of the Siberian roe deer (Capreolus pygargus) that possess up to 14 B chromosomes to investigate the presence and expression of genes on supernumerary chromosomes.
Here, we describe a 2 Mbp region homologous to cattle chromosome 3 and containing TNNI3K (partial), FPGT, LRRIQ3 and a large gene-sparse segment on B chromosomes of the Siberian roe deer. The presence of the copy of the autosomal region was demonstrated by B-specific cDNA analysis, PCR assisted mapping, cattle bacterial artificial chromosome (BAC) clone localization and quantitative polymerase chain reaction (qPCR). By comparative analysis of B-specific and non-B chromosomal sequences we discovered some B chromosome-specific mutations in protein-coding genes, which further enabled the detection of a FPGT-TNNI3K transcript expressed from duplicated genes located on B chromosomes in roe deer fibroblasts.
Discovery of a large autosomal segment in all B chromosomes of the Siberian roe deer further corroborates the view of an autosomal origin for these elements. Detection of a B-derived transcript in fibroblasts implies that the protein coding sequences located on Bs are not fully inactivated. The origin, evolution and effect on host of B chromosomal genes seem to be similar to autosomal segmental duplications, which reinforces the view that supernumerary chromosomal elements might play an important role in genome evolution.
大多数真核生物的染色体组型稳定，具有特定的二倍体数量。B 染色体是标准染色体组型之外的额外染色体，即使在同一个体的细胞之间，其大小、数量和形态也可能有所不同。多年来，人们普遍认为存在于一些植物、动物和真菌物种中的 B 染色体缺乏活性基因。最近，分子细胞遗传学研究表明，B 染色体上存在额外的蛋白质编码基因拷贝。然而，这些基因的转录活性仍然难以捉摸。我们研究了拥有多达 14 条 B 染色体的西伯利亚狍的染色体组型，以研究超数染色体上基因的存在和表达。
在这里，我们描述了一个与牛染色体 3 同源的 2 Mbp 区域，该区域包含 TNNI3K（部分）、FPGT、LRRIQ3 和一个大型基因稀疏片段，位于西伯利亚狍的 B 染色体上。通过 B 染色体特异性 cDNA 分析、PCR 辅助作图、牛细菌人工染色体（BAC）克隆定位和定量聚合酶链反应（qPCR），证明了该染色体区域的存在。通过 B 染色体特异性和非 B 染色体序列的比较分析，我们在蛋白质编码基因中发现了一些 B 染色体特异性突变，这进一步使我们能够检测到来自 B 染色体的 FPGT-TNNI3K 转录本，该转录本是在狍纤维母细胞中位于 B 染色体上的重复基因表达的。
在西伯利亚狍的所有 B 染色体中发现一个大的常染色体片段进一步证实了这些元件的常染色体起源。在纤维母细胞中检测到 B 衍生的转录本意味着位于 Bs 上的蛋白质编码序列没有完全失活。B 染色体基因的起源、进化及其对宿主的影响似乎与常染色体片段重复相似，这进一步证明了超数染色体元件可能在基因组进化中发挥重要作用。
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