- Col1a1 promoter-targeted expression of p20 CCAAT enhancer-binding protein beta (C/EBPbeta), a truncated C/EBPbeta isoform, causes osteopenia in transgenic mice. Harrison, J.R., Huang, Y.F., Wilson, K.A., Kelly, P.L., Adams, D.J., Gronowicz, G.A., Clark, S.H. J. Biol. Chem. (2005)