IN-VIVO AND IN-VITRO EXPRESSION OF A NONMAMMALIAN CYCLOOXYGENASE-1

Unlike cyclooxygenase 2 (COX-2), COX-I has never been identified, puri fied or cloned in a non-mammalian species. Here we report the RT-PCR c loning of a chicken cDNA that encodes the amphipathic membrane binding region and parts of the dimerization and catalytic domains of COX-1-l ike enzyme. Sequence comparison showed this putative COX-I to be evolu tionarily less conserved than COX-2. Furthermore, whereas COX-I in mam mals is broadly expressed in tissues as a constitutive enzyme, the mRN A detected by our clone in chicken was almost absent in tissues and em bryo fibroblasts (CEF). Highest expression was in brain and seminal ve sicle. This transcript was not detectable during chick embryogenesis a nd, as is the case for mammalian COX-I, was not induced above backgrou nd by mitogen stimulation. The identification of an avian COX-1 shows that COX-I and COX-2 existed as separate catalysts for prostaglandin s ynthesis before the divergence of birds and mammals.