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Summary

Gla-rich protein (GRP, also known as UCMA for upper zone of growth plate and cartilage matrix associated protein), a novel vitamin K-dependent (VKD) protein, has been identified and isolated from sturgeon by our group and found to have orthologs in nearly all taxonomic groups of vertebrates (named GRP1) and a paralog in bony fish (named GRP2). Additional evidence supporting this hypothesis was recently obtained in zebrafish through analysis of the genomic environment of its 2 grp genes compared to that of the mouse gene. Data confirmed that fish and mammalian GRP genes are true orthologs and that the two zebrafish genes result from ancestral genomic fragment duplication now located in zebrafish chromosomes 4 and 25. In sturgeon, as well as during mouse development, cartilaginous tissues or their precursors are primary sites of GRP expression. Recently, our laboratory has shown that GRP is a circulating protein also expressed and accumulated in some soft tissues and clearly associated with ectopic calcification events. Since this protein has the highest Gla density of any known VKD protein, it was proposed that GRP might be a potent physiological modulator of soft tissue calcification. Contradictory functional studies have recently been published for grp. While in zebrafish recent data indicated a role of Grp-1 (Ucmaa) during zebrafish skeletal development, another recent genetic study using a knockout strategy failed to identify a relevant function for grp during mouse development. Therefore, further studies are required in order to understand this discrepancy and provide insight into grp function and the molecular players involved in its regulation. In the present work we have taken a computational approach to identify cis-regulatory transcription factor (TF) binding motifs in both grp1/ucmaa and grp2/ucmab genes from two model fish with compact and well characterized genomes, the fugu (Takifugu rubripes) and the tetraodon (Tetraodon nigroviridis). By comparing promoters from ortholog genes we expected to define conserved transcriptional motifs indicative of regulatory networks affecting these genes. Accordingly, our computational methods identified several TFs, whose binding profiles are available in the TRANSFAC database, which can be important for the regulation of these two genes.