Comparative analysis of a BAC contig of porcine chromosome 13q31-q32 and human chromosome 3q21-q22

Abstract

Background: The gene(s) encoding the ETEC F4ab/ac receptors, involved in neonatal diarrhoea in pigs (a disease not yet described in humans), is located close to the TF locus on Sscr13. In order to reveal and characterize possible candidate genes encoding these receptors, a porcine physical map of the TF region is indispensable.

Results: A contig of 33 BAC clones, covering approximately 1.35 Mb surrounding the TF locus on Sscr13q31-q32, was built by chromosome walking. A total of 22,552 bp from the BAC contig were sequenced and compared with database sequences to identify genes, ESTs and repeat sequences, and to anchor the contig to the syntenic region of the human genome sequence (Hsap3q21-q22). The contig was further annotated based on this human/porcine comparative map, and was also anchored to the Sanger porcine framework map and the integrated map of Sscr13 by RH mapping.

Conclusion: The annotated contig, containing 10 genes and 2 ESTs, showed a complete conservation of linkage (gene order and orientation) with the human genome sequence, based on 46 anchor points. This underlines the importance of the human/porcine comparative map for the identification of porcine genes associated with genetic defects and economically important traits, and for assembly of the porcine genome sequence.

Figure 1

Comparative map of the annotated BAC contig with its syntenic region on Hsap3q21-q22. The contig is drawn in part C. Black triangles represent BAC end sequences from which primers were designed to construct the contig. The black circle represents the only internal BAC sequence from which primers were designed to construct the contig. White circles show overlaps of these BAC sequences with other BAC clones. White triangles represent BESs from which it was impossible to design primers. The triangles point towards the 3'-side of the BAC clone. Encircled triangles represent BAC ends that are also present in the Sanger framework map. Black diamonds represent microsatellite positions. Black squares represent genes annotated by PCR, whereas white squares represent genes annotated by hybridization. Annotated sequences (genes are in regular, ESTs in italic) from the BAC contig are represented on a plane map (B) and their homology with the human genome sequence is illustrated with dotted lines (A). The orientation of the human genes and finished HTGs (used to assemble the human genome sequence) are represented in (A) by arrows [10]. Repeat sequences (white rectangle = LINE, black rectangle = SINE, black bow = LTR element, white bow = DNA element) are shown on a plane map in D. The RH mapping results are shown in E.