Mutation of a ubiquitously expressed mouse transmembrane protein (Tapt1) causes specific skeletal homeotic transformations.

L5Jcs1 is a perinatal lethal mutation uncovered in a screen for ENU-induced mutations on mouse chromosome 5. L5Jcs1 homozygotes exhibit posterior-to-anterior transformations of the vertebral column midsection, similar to mice deficient for Hoxc8 and Hoxc9. Positional cloning efforts identified a mutation in a novel, evolutionarily conserved, and ubiquitously expressed gene dubbed Tapt1 (Transmembrane anterior posterior transformation 1). TAPT1 is predicted to contain several transmembrane domains, and part of the gene is orthologous to an unusual alternatively spliced human transcript encoding the cytomegalovirus gH receptor. We speculate that TAPT1 is a downstream effector of HOXC8 that may act by transducing or transmitting extracellular information required for axial skeletal patterning during development.