The present invention is based, in part, on our discovery of compositions and methods that can be used to treat a patient who has a compromised bone (due, for example, to a disease such as osteoporosis or an injury such as a bone fracture). The compositions can also be administered prophylactically. For example, they can be administered to help maintain bone health as a patient ages. More specifically, the compositions include polypeptides that constitute (or that include) a fragment of a calcitonin receptor (CR) and polypeptides that constitute (or include) biologically active variants of those fragments. Sequence-specific formulas are provided herein, and polypeptides conforming to those formulas, as well as nucleic acids encoding them, expression vectors, host cells, pharmaceutical formulations, and methods of their preparation and use are within the scope of the present invention.
