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

Abstract

BackgroundMost 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.ResultsHere, 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.ConclusionsDiscovery 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.

Characterization of maize B-chromosome-related transcripts isolated via cDNA-AFLP

“…In Drosophila albomicans, an actively transcribed unit of the B-chromosome was identified, which showed sequence homology with the subcentromeric region of both the ancient X and neo-X chromosomes (Zhou et al 2012). In the Siberian roe deer, Capreolus pygargus, three A-chromosome-located genes were found on the B-chromosome, one of which was transcribed in fibroblast culture (Trifonov et al 2013).…”

Identification of polymorphisms and transcriptional activity of the proto-oncogene KIT located on both autosomal and B chromosomes of the Chinese raccoon dog

“…In addition, some protein-coding genes have also been identified on the B chromosomes of certain species (Miao et al, 1991;Lamatsch et al, 2011;Yoshida et al, 2011;Martis et al, 2012). Some of these are thought to have functional significance for their host (Miao et al, 1991;Yoshida et al, 2011) and exhibit transcriptional activity (Trifonov et al, 2013).…”

B chromosomes showing active ribosomal RNA genes contribute insignificant amounts of rRNA in the grasshopper Eyprepocnemis plorans

“…In addition, Carchilan et al (2009) showed, in rye, the presence of B-specific transcribed DNA sequences belonging to highcopy families with similarity to mobile elements, and Zhou et al (2012) have characterized a B chromosome-linked scaffold that contains an actively transcribed unit. Recently, it has been shown the transcription of a protein-coding gene on B chromosomes of the Siberian roe deer (Capreolus pygargus) (Trifonov et al 2013) and Banaei-Moghaddam Abstract The genetic inertness of supernumerary (B) chromosomes has recently been called into question after finding several cases of gene activity on them. The grasshopper Eyprepocnemis plorans harbors B chromosomes containing large amounts of ribosomal DNA (rDNA) units, some of which are eventually active, but the amount of rRNA transcripts contributed by B chromosomes, compared to those of the standard (A) chromosomes, is unknown.…”