Genomic organization and chromosome localization of the murine homeobox gene Pmx

Homeobox genes are expressed in very specific temporal and spatial patterns and function as transcriptional regulators of developmental processes. The murine homeobox gene, Pmx (paired mesoderm homeobox), is expressed in a mesodermally restricted pattern in embryos and most abundantly in cardiac, skeletal, and smooth muscle tissues in adults. Previously, this murine gene was named K-2 and mHox, while the human homolog was named Phox1. In this report, the localization of Pmx has been determined by interspecific backcross analysis. The Pmx gene is located on Chromosome 1, approximately 3.3 cM distal to the Gsh-4 homeobox locus. The sequence of the Pmx transcript has been extended toward the 5' end and corresponds in size to one of the transcripts previously detected by Northern blot analysis. Sequence analysis indicates that Pmx is the first characterized mammalian gene to encode a paired type homeodomain, but not a paired domain. The Pmx gene includes at least five exons spanning a minimum of 60 kb of genomic DNA, making this the largest known murine homeobox gene.