One aspect of the invention relates to a novel human cDNA, called TIG1 (Tazarotene Induced Gene 1). Expression of the corresponding TIG1 mRNA is strongly induced from a low basal level upon treatment of skin raft cultures with the RAR .beta./.gamma. selective anti-psoriatic synthetic retinoid AGN-190168 (ethyl 6-[2-(4,4) dimethyl-thiochroman-6-yl] ethynyl-nicotinate). The TIG1 mRNA is also up-regulated by AGN-190168 and the acid form AGN-190299 (6-[2-(4,4) dimethyl-thiochroman-6-yl] ethynyl-nicotinic acid) in skin raft cultures prepared from psoriatic fibroblasts and normal keratinocytes. Further, the TIG1 mRNA is similarly up-regulated by AGN-190168 in primary fibroblast and keratinocyte cultures. The low basal expression of the TIG1 mRNA is particularly advantageous when used as an indicator of retinoid action in psoriatic skin culture systems. Assay systems employing this unique TIG1 expression profile are disclosed.