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Open Access Research article

Transcription of a protein-coding gene on B chromosomes of the Siberian roe deer (Capreolus pygargus)

Vladimir A Trifonov1*, Polina V Dementyeva1, Denis M Larkin2, Patricia CM O’Brien3, Polina L Perelman1, Fengtang Yang4, Malcolm A Ferguson-Smith3 and Alexander S Graphodatsky1

  • * Corresponding author: Vladimir A Trifonov vlad@mcb.nsc.ru

  • † Equal contributors

Author Affiliations

1 Institute of Molecular and Cellular Biology SВ RAS, Novosibirsk, Russia

2 Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, UK

3 Cambridge Centre for Comparative Genomics, Department of Veterinary Medicine, University of Cambridge, Cambridge, UK

4 Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, UK

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BMC Biology 2013, 11:90  doi:10.1186/1741-7007-11-90

Published: 6 August 2013

Abstract

Background

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.

Results

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.

Conclusions

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.

Keywords:
B chromosomes; Segmental duplications; Gene duplications; Karyotype evolution; Cervidae