15-P027 Role of Hox genes in walking leg morphology specification in insects and spiders

Vertebrates have evolved gills and homologous organ parathyroid that regulate calcium level in the blood in their different living environments. In higher teleosts, chloride cells in the skin are known to regulate calcium level, yet molecular mechanisms that control development of these cells during the evolution of higher teleosts remain to be investigated. We discuss a possible role of the evolution of Gcm2 enhancers in an acquisition process of a novel calcium-regulating organ. Our studies have revealed that Gcm2 was expressed not only in parathyroid and gills but also in chloride cells of zebrafish. The antisense morpholino of Gcm2 abolished development of chloride cells, suggesting that Gcm2 might be essential for their development. To examine further a role of Gcm2 in development of the chloride cells, we analyzed enhancer elements of Gcm2 and candidate upstream genes of Gcm2. We identified two enhancer regions controlling Gcm2 expression in chloride cells of zebrafish, although the similar enhancers have not been found in other vertebrates. One enhancer region contains a possible motif for the protein-binding site of Foxi3 (known to be essential for chloride cell development). We are now analyzing whether Foxi3 is a potential upstream gene of Gcm2 and determining if two enhancers of Gcm2 along with Foxi3 gene might have be responsible for evolution of chloride cells in zebrafish.