THE BIFUNCTIONAL PROTEIN DCOH PCD, A TRANSCRIPTION FACTOR WITH A CYTOPLASMIC ENZYMATIC-ACTIVITY, IS A MATERNAL FACTOR IN THE RAT EGG AND EXPRESSED TISSUE SPECIFICALLY DURING EMBRYOGENESIS/

The bifunctional protein DCoH/PCD is both a cytoplasmatic enzyme (PCD) involved in the tetrahydrobiopterin regeneration and a transcription coactivator (DCoH). Originally detected in liver cell nuclei, it forms a 2:2 heterotetrametric complex with the nuclear transcription factor s HNF1 alpha and the variant form HNF1 beta and enhances their transcr iptional potential. To address the role of DCoH in tissue specific and developmental gene regulation we analyzed its spatial and temporal ex pression pattern in the rat. DCoH might have a function in tissue spec ific gene expression mediated by HNF1 in the adults and in the develop ing embryo as it is found in the kidney and the liver, organs known to contain HNF1. In addition DCoH is a maternal factor in the rat egg la cking HNF1 transcription factors. The maternal protein enters the cell nuclei at the 8-cell stage suggesting a role in early embryonic gene regulation and excluding a cytoplasmatic enzymatic function. Evidence for a HNF1 independent function of DCoH is also given by the fact that DCoH is present in the eyes (pigmented epithelium) and the brain (epe ndym cells) of the rat embryos, cell types lacking HNF1 proteins. The tightly regulated expression pattern of DCoH in distinct cell types or iginating from endo- meso- and ectoderm is conserved between the rat a nd the frog indicating a fundamental role for DCoH in early gene regul ation among the vertebrates.