The present invention relates to methods, agents and compound screening assays for inducing differentiation of undifferentiated mammalian cells into osteoblasts. The invention thus provides a method, comprising contacting a compound with a polypeptide comprising an amino acid sequence selected from the group consisting of SEQ ID No: 194-309; and measuring a compound-polypeptide property related to the differentiation of said cells. The invention further relates to a bone formation enhancing pharmaceutical composition, and the use thereof in treating and/or preventing a disease involving a systemic or local decrease in mean bone density in a subject. Furthermore, the invention relates to a method for the in vitro production of bone tissue.