Hox C cluster genes are dispensable for overall body plan of mouse embryonic development

Hox genes encode transcription factors which provide positional information during morphogenesis along the body axis; genetic interaction among Hox genes is thought to be necessary for correct pattern formation. One of the most curious features of the 39 vertebrate Hox genes is that they form four clusters each composed of several genes paralogous between clusters. This raises the question are all four clusters necessary for the development of vertebrates and, if so, what is the function of each cluster? To provide an answer to this question, we prepared Hox C cluster null mice utilizing the Cre-loxP system. Hox C cluster null mice, lacking all nine Hox C genes, die at the time of birth; however, the mutant pups develop to this stage with minor transformations. This development shows that the Hox C genes are dispensable for the overall body plan of mouse embryogenesis. Furthermore, transformations observed in the skeletal system of the Hox C cluster null mice are milder than those observed in the Hoxc-9 null mice, providing further evidence that at least some genes within a cluster exhibit interaction functions with each other.