REFINEMENT OF BOVINE CHROMOSOME-2 LINKAGE MAP NEAR THE MH LOCUS REVEALS REARRANGEMENTS BETWEEN THE BOVINE AND HUMAN GENOMES

The locus responsible for the appearance of muscular hypertrophy (mh) in double muscled cattle breeds has recently been shown to encode a se creted growth factor designated myostatin (MSTN). This conclusion was based in part on the placement of MSTN in the interval to which mh had been mapped on bovine chromosome 2 (BTA2). During the mapping phase o f the study, numerous yeast artificial chromosome (YAC) clones were is olated that contained genetic markers closely linked to mh. Other YACs and cosmids were identified that contained genes selected from human chromosome 2q (HSA2q), with the goal of defining the position of break points in conserved synteny between the bovine and human comparative m aps, thereby permitting accurate selection of positional candidate gen es, An efficient subcloning procedure was developed to obtain microsat ellites [ms) from YAC clones, to increase the number of informative me ioses in herds segregating for mh. The same procedure was used to plac e the human orthologues of engrailed-l (EN1), interleukin 1 beta (IL1B ), and paired-box-containing 8 (PAX8) genes on the cattle map to furth er define the positions of breakpoints in conserved synteny and gene o rder. Twenty-three of 28 ms identified fled om YAC subclone libraries were informative in the mapping families. Seven mapped to the centrome ric end of BTA2, which contains the mh locus, improving marker density and informativeness. The two MSTN and four EN1 gene-associated ms mar kers developed from YACs, map to positions 1.5 and 61.6 CM in the BTA2 linkage group, respectively, In addition, ms markers developed from c osmids containing either IL1B or PAX8, map to positions 56.6 and 56.9 CM in the BTA11 linkage group, respectively. . These linkage data conf irm the location and orientation of orthologous segments of HSA2q that were previously indistinguishable on the bovine map, and demonstrates the presence of microrearrangements of gene order (segments <10 CM) a nd conserved synteny between the human and bovine genomes.