GPRC6A and Insulin resistance: GPRC6A was only expressed in the Leydig cells of the testes and not in follicular cells of the ovary.43,114 Furthermore, mutation and polymorphisms of the human GPRC6A gene was associated with insulin resistance and failure of testis function, which were also observed in Ocn-deficient mice.132,138 These facts together confirm that GPRC6A transduces OCN signals in the testes (Fig. 4).