INSERTION OF A TARGETING CONSTRUCT IN A HOXD-10 ALLELE CAN INFLUENCE THE CONTROL OF HOXD-9 EXPRESSION

A neomycin resistance (neo) gene driven by the phosphoglycerokinase (P GK) promoter was inserted into the Hoxd-10 homeobox by homologous reco mbination in embryonic stem (ES) cells. Chimeric mice derived from ES cell-injected blastocysts died shortly after birth. Craniofacial and a xial abnormalities were found in the skeleton of these chimeras, resem bling some of the previously described Hox gene gain-of-function pheno types. The spatial expression patterns of various Hoxd gene transcript s were analysed in chimeric mutant embryos by in situ hybridization. T wo main observations were made: (1) a wide ectopic expression domain o f the Hoxd-9 gene was found in the spinal cord of these embryos, and ( 2) the neo gene exhibited a specific Hox-like expression domain which extended far more rostrally than that of the Hoxd-10 gene, showing tha t, in the context of this mutation, the PGK promoter could be regulate d as a Hox promoter. These results provide the first evidence that a t argeted insertion into a Hox gene coding sequence, in the context of i ts own cluster, could result in misexpression of a neighbour gene of t he complex. (C) 1994 Wiley-Liss, Inc.