Expression of growth/differentiation factor 1 in the nervous system: conservation of a bicistronic structure

Growth/differentiation factor 1 (GDF-1) is a recently described member of the transforming growth factor beta superfamily isolated from a day-8.5 mouse embryo cDNA library. Northern (RNA) analysis of embryonic mRNA detected two GDF-1 transcripts [1.4 kilobases (kb) and 3.0 kb in length] displaying distinct temporal patterns of expression. Only the 3.0-kb transcript was detected in adult tissues, where its expression was restricted almost exclusively to the central nervous system. Comparison of murine and human brain cDNA sequences corresponding to the 3.0-kb transcript revealed high conservation of two nonoverlapping open reading frames with poor conservation of the intervening spacer region and the putative 5' and 3' untranslated sequences. By immunohistochemical analysis, the protein encoded by the downstream open reading frame (GDF-1) was detected exclusively in the brain, spinal cord, and peripheral nerves in day-14.5 mouse embryos. The upstream open reading frame encodes a protein of unknown function containing multiple putative membrane-spanning domains. These findings raise the possibility that this mRNA may give rise to two different proteins.