The DE-retinoic acid response element located 3' of Hoxb5 was replaced with a floxed neo cassette. Cre mediated recombination removed the neo cassette. RT-PCR analysis indicates significant down regulation of expression of Hoxb1, Hoxb5 and Hoxb6 in the hindbrain and spinal cord from homozygous mice. (J:208763)