Loss of cped1 does not affect bone and lean mass in zebrafish.

Human genetic studies have nominated Cadherin-like and PC-esterase Domain-containing 1 ( CPED1 ) as a candidate target gene mediating bone mineral density (BMD) and fracture risk heritability. Recent efforts to define the role of CPED1 in bone in mouse and human models have revealed complex alternative splicing and inconsistent results arising from gene targeting, making its function difficult to interpret. To better understand the role of CPED1 in adult bone mass and morphology, we turned to zebrafish, an emerging model for orthopaedic research. We analyzed two different cped1 mutant lines and performed deep phenotyping to characterize more than 200 measures of adult vertebral, craniofacial, and lean tissue morphology. We also examined alternative splicing of zebrafish cped1 and gene expression in various cell/tissue types. Our studies fail to support an essential role of cped1 in adult zebrafish bone. Specifically, homozygous mutants for both cped1 mutant alleles, which are expected to result in loss-of-function and impact all cped1 isoforms, exhibited no significant differences in the measures examined when compared to their respective wildtypes, suggesting that cped1 does not significantly contribute to these traits. We identified sequence differences in critical residues of the catalytic triad between the zebrafish and mouse orthologs of CPED1, and discuss how these differences, as well as distinct alternative splicing, could underlie different functions of CPED1 orthologs in the two species. Our studies demonstrate that cped1 is not required for normal adult zebrafish bone mass, lean mass, or bone and lean mass morphology, adding to evidence that variants at 7q31.31 can act independently of CPED1 to influence BMD and fracture risk.