At the crossroads of developmental genetics: the cloning of the classical mouse T locus

The discovery, more than 60 years ago, of a mutant mouse with a short tail led to the birth of the new field of developmental genetics. Over the years since, numerous investigators have probed the biology of the original short-tail mutation at the T locus, as well the naturally-occurring t haplotypes that were uncovered as a result of their interaction with this mutation. Although the T locus ranks among the best characterized developmental loci in the mouse, it was not among the first to be cloned. This situation has now been rectified with two recent reports from Herrmann, Lehrach and their colleagues. While the T locus is expressed uniquely in the embryonic tissues predicted from the mutant phenotype, the gene itself, as well as the predicted amino acid sequence of the T product, show no strong homology to any known sequence. For the moment, at least, the mystery behind the function of the T locus still awaits definitive resolution.