Molecular characterization of two paralog genes encoding Gla-rich protein (Grp) in zebrafish

Summary

Gla-rich protein (GRP) is a novel vitamin K-dependent protein with the highest Gla content of any protein known to date that has been identified in all taxonomic groups of vertebrates (named GRP1) with a paralog in bony fish (named GRP2). In sturgeon, as well as during mouse development, cartilaginous tissues or their precursors are primary sites of GRP expression. In this article, we identify two grp isoforms, grp1 and grp2, encoded by two distinct genes localized in zebrafish chromosomes 25 and 4, respectively. These two genes span, respectively, 6 kb and 9 kb of genomic DNA and are both composed of five exons. Within the coding regions, the overall amino acids identity is 48.6 and 42.0%, respectively, for Grp1 and Grp2 compared to the human GRP. We also have identified the presence of splice variants already previously described in mouse, and corresponding expression levels were determined during embryonic stages and in different adult tissues. The levels of grp expression appear to be inversely correlated, with grp1 being expressed first and remaining high during early development while expression of grp2 appears later and increases in late larval and juvenile stages, having greater prevalence in adult tissues. We conclude that in zebrafish, grp paralogs exhibited distinct patterns of expression suggesting different regulatory pathways for each gene.