The mouse plasminogen locus maps to the recombination breakpoints of the tLub2 and TtOrl partial t haplotypes but is not at the tw73 locus

Abstract

The mouse plasminogen (Plg) locus maps to a region of chromosome (Chr) 17 which is inverted in the t haplotype Chromosomal variant. Here we investigate the genomic organization of the Plg locus in structurally variant forms of Chr 17; wild-type (+), t haplotype (t), and two partial t haplotypes TtOrl and tLub2 which arose by recombination between + and t chromosomes. Our analysis suggests that the t haplotype chromosomal variant contains extra, inverted copies of the Plg locus, and that a single locus is present in the wild-type variant. Changes in the Plg locus in TtOrl and tLub2 suggest that they arose by homologous recombination across elements in the Plg locus having the same orientation in the wild-type and t haplotype chromosomes. One hundred ten kb around the wild-type Plg genomic locus have been cloned and the proximal breakpoint of a deletion in the tLub2 chromosome has been localized to a fragment 30 kb downstream of the Plg gene. The tLub2 deletion has been shown to delete a gene named tw73 that affects blastocyst implantation, a process probably requiring proteases such as plasminogen. However, the mapping of Plg relative to the tLub2 deletion and mRNA analysis of plasminogen in tw73 heterozygotes suggests that Plg does not lie at the tw73 locus.