Zic Genes in Teleosts: Their Roles in Dorsoventral Patterning in the Somite.

The medaka contains seven zic genes, two of which, zic1 and zic4, have been studied extensively. The analyses are mainly based on the double anal fin (Da) mutant, which was isolated from the wild. Da is an enhancer mutant of zic1/zic4, and the expression of zic1/zic4 is specifically lost in the dorsal half of the somites, which leads to a mirror-image duplication of the ventral half across the lateral midline from larva to adult. The studies of medaka Da give us important insights into the function of zic1/zic4 in mesodermal tissues and also the mechanism of dorsoventral patterning in the vertebrate trunk region occurring during late development, which is a long-standing mystery in developmental biology. In this chapter, we introduce genomic organization of medaka zic genes and discuss their function, mainly focusing on zic1 and zic4 in dorsoventral patterning of the trunk region and possible connections to human congenital disorders.