TOB1 and osteoporosis: Tob as a co-repressor is another negative regulator of BMP/Smad signaling in osteoblasts.173 BMP2-signal is elevated in the absence of Tob and repressed by overproduction of Tob.174,175 Mice carrying a targeted deletion of the Tob gene had a greater bone mass resulting from increased numbers of osteoblasts and were protected from OVX-induced osteoporosis.174,175