We have generated and characterized OGR1-deficient mice to address several critical issues: 1) the physiological functions of OGR1 in mice; 2) the role of OGR1 in osteoclastogenesis; 3) the OGR1-dependent pH responsiveness using OGR1-deficient cells; and 4) the functions of OGR1 in other bone biological processes when mice are challenged by exogenous stimuli, such as tumor cells. Here, GPR68 is linked to neoplasm.