Retinoid signaling system is composed of retinoic acids, retinol binding proteins (RBPs ), cellular retinol binding proteins (CRBPs), cellular retinoic acid binding proteins (CRABPs), retinoic acid nuclear receptors and retinoic acid responsible elements. This system has been proved to regulate expression of many functionillg genes, such as genes of CRABP- I,c-Fos, growth factor receptor, protein kinase C,etc. Therefore, the retinoid's role in morphogenesis during embryonic development and regulating the growth and differentiation of a wide varity of cell types throughout life of organism are involved in this signaling system.