Gene and cluster-specific expression of the Iroquois family members duringmouse development

Mammalian homologues of the Drosophila Iroquois homeobox gene complex, invo lved in patterning and regionalization of differentiation, have recently be en identified (Mech. Dev., 69 (1997) 169; Dev. Biol., 217 (2000) 266; Dev. Dyn., 218 (2000) 160; Mech. Dev., 91 (2000) 317; Dev. Biol., 224 (2000) 263 ; Genome Res., 10 (2000) 1453; Mech. Dev., 103 (2001) 193). The six members of the murine family were found to be organized in two cognate clusters of three genes each, Irx1, -2, -4 and Irx3, -5, -6, respectively (Peters et a l.. 2000). As a basis for further study of their regulation and function we performed a comparative analysis of the genomic organization and of the ex pression patterns of all six Irx genes. The genes are expressed in highly s pecific and regionalized patterns of ectoderm, mesoderm and endoderm derive d tissues. In most tissues the pattern of expression of the clustered genes , especially of Irx1 and -2 and of Irx3 and -5, respectively, closely resem bled each other while those of Irx4 and -6 were very divergent. Interesting ly, the expression of cognate genes was found to be mutually exclusive in a djacent and interacting tissues of limb, heart and the laryncho-pharyncheal region. The results indicate that the Irx genes are coordinately regulated at the level of the cluster. (C) 2001 Elsevier Science Ireland Ltd. All ri ghts reserved.