Tosta Vander C, Marthe Jefferson B, Tavares Mara G, Fernandes-Salomão Tânia M, Pompolo Silvia G, Recco-Pimentel Shirlei M, Perfectti Francisco, Campos Lucio A O, Camacho Juan Pedro M
Departamento de Biologia Geral, Universidade Federal de Viçosa, Viçosa, Brazil.
Cytogenet Genome Res. 2014;144(3):220-6. doi: 10.1159/000370171. Epub 2015 Jan 20.
The origin of supernumerary (B) chromosomes is still a debated topic, with intra- and interspecific origins being the most plausible options. In the bee Partamona helleri, a sequence-characterized amplified region (SCAR) marker being specific to B chromosomes suggested the possibility of interspecific origin. Here, we search for this marker in 3 close relative species and perform DNA sequence comparison between species. The SCAR sequence does not show homology with other sequences in the databases, but does contain an open reading frame with sequence homology with a reverse transcriptase. Dot-blot hybridization using the SCAR marker as a probe confirmed that it is present in B-carrying, but not B-lacking larvae of P. helleri, and indicated its presence in adult individuals of P. cupira and P. criptica. Additionally, PCR amplification of the SCAR marker was successful on genomic DNA obtained from P. helleri and P. rustica larvae carrying B chromosomes, and on genomic DNA obtained from adult individuals of P. cupira, P. criptica and P. rustica. Finally, a comparison of the DNA sequence of the SCAR markers amplified from these 4 species showed very few nucleotide differences between the species. The complete association between B chromosome and SCAR presence and the scarce divergence observed for this DNA sequence between the 4 species analyzed suggest the possibility that this B chromosome has recently been transferred between species through several episodes of interspecific hybridization.
多余（B）染色体的起源仍然是一个有争议的话题，种内和种间起源是最有可能的选项。在蜜蜂Partamona helleri中，一个对B染色体特异的序列特征扩增区域（SCAR）标记表明了种间起源的可能性。在这里，我们在3个近缘物种中寻找这个标记，并进行物种间的DNA序列比较。SCAR序列与数据库中的其他序列没有同源性，但确实包含一个与逆转录酶具有序列同源性的开放阅读框。使用SCAR标记作为探针的点杂交证实，它存在于携带B染色体的Partamona helleri幼虫中，而不存在于不携带B染色体的幼虫中，并表明它存在于P. cupira和P. criptica的成虫个体中。此外，从携带B染色体的Partamona helleri和P. rustica幼虫获得的基因组DNA，以及从P. cupira、P. criptica和P. rustica成虫个体获得的基因组DNA上，SCAR标记的PCR扩增均成功。最后，对从这4个物种扩增的SCAR标记的DNA序列进行比较，发现物种之间的核苷酸差异非常少。B染色体与SCAR存在之间的完全关联，以及在所分析的4个物种之间该DNA序列观察到的极少差异，表明这种B染色体最近可能通过几次种间杂交事件在物种间转移。
