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 in bone difficult to interpret. To better understand the role of CPED1 in adult bone mass and morphology, we conducted a comprehensive genetic and phenotypic analysis of cped1 in zebrafish, an emerging model for bone and mineral 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 wildtype controls, 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, suggesting that differences in key residues, as well as distinct alternative splicing, could underlie different functions of CPED1 orthologs in the two species. Our studies fail to support a requirement of cped1 in zebrafish bone and lean tissue, adding to evidence that variants at 7q31.31 can act independently of CPED1 to influence BMD and fracture risk. Lay summaryBone mineral density (BMD) is a key indicator for predicting and diagnosing osteoporosis and fracture risk, and it has been estimated that up to 89% of variation in BMD is determined by genetics. Multiple human genetics studies have nominated CPED1 as a potential gene underlying BMD and fracture risk heritability, however the function of CPED1 remains poorly understood. In this study, we examined the role of cped1 in bone by quantifying over 200 morphological measures of vertebral and craniofacial bone size, shape, and density in two different mutant lines of zebrafish in which cped1 function was reduced or eliminated. We also examined lean tissue mass because co-heritability of this trait with BMD has also been hypothesized to involve CPED1. Surprisingly, despite the loss of cped1 function, there were no significant differences between the mutant zebrafish and their respective controls. Our study therefore fails to support a role for cped1 in bone and lean tissue, suggesting that hereditary influence on BMD and fracture risk can occur independently of CPED1.