Gene deletion and functional analysis of Fetuin-B

This study aimed at elucidating the physiological function of the serum protein fetuin-B and comparing it with its closest family member fetuin-A. Fetuin-A is known to be an inhibitor of calcium and phosphate precipitation in vivo. This has been shown in a fetuin-A-deficient animal model. In this study, the serum protein fetuin-B was deleted in an animal model to analyze its effect on the organism. The analysis of the fetuin-B-deficient mice revealed that fetuin-B was essential for fertilization. Female fetuin-B-deficient mice failed to produce any offspring when mated with any genotype. Heterozygous fetuin-B-deficient female mice and males of any genotype were reproductive, however. The main finding of this study was that oocytes derived from naturally mated fetuin-B-deficient female mice did not reveal any fertilization characteristics and did not develop to two-cell pre-implantation embryos in vitro, indicating a fertilization defect. It remains to be clarified whether fetuin-B is required as a structural, a catalytic, or a transport protein. In this study a novel target for fertilization control was identified: fetuin-B. Further characterization of the fetuin-B-deficient mice did not reveal any abnormalities with regard to their anatomy, morphology, physiological parameters or metabolic functions. It remains to be studied if the fetuin-B-deficient mice develop disease when challenged or stressed. Fetuin-B was cloned and expressed eukaryotically as a recombinant fusion protein. Functional in vitro assays performed with the purified recombinant fetuin-B showed that it could not compensate for fetuin-A deficiency, as shown by their distinct calcium phosphate precipitation inhibiting potential. As for the fetuin-A- and fetuin-B-deficient animal models, both exhibit distinct phenotypes and differ completely in their most prominent phenotypes: fetuin-A deficiency leads to ectopic calcification, while fetuin-B deficiency leads to female infertility. The data provided by this study thus clearly suggests that the fetuin-family members have distinct functions in vivo