Transgenic and Gene Knock-Out Animals in Skeletal Research

Abstract

Until recently most of our knowledge about the skeleton was derived from descriptive morphology, histomorphometry, endocrinology, and cellular studies of bone turnover (Delling 1987; Delling and Amling 1995; Amling et al. 1994, 1996). Recent approaches have led to the identification of local factors that regulate skeletal morphogenesis. Molecular and biochemical studies of bone cells in vitro and, most importantly, the power of genetics entering the bone field have led us toward the beginning of a molecular understanding of the skeletal system (Erlebacher et al. 1995). Indeed the identification of genes responsible for mouse and human skeletal abnormalities, gene inactivation and targeted gene misexpression in mice have documented the importance of specific signaling molecules and their receptors, as well as growth factors, matrix proteins, and transcription factors in the development and maintenance of bone. The successful convergence of mouse and human genetics in skeletal biology has been demonstrated several times, e.g. chondrodysplasia in parathyroid hormone-related protein (PTHrP) receptor mutant mice (Amizuka et al. 1994; Karaplis et al. 1994; Lanske et al. 1996; Weir et al. 1996; Amling et al. 1997) and patients with Jansens metaphyseal dysplasia (Schipani et al. 1995). Mutations in collagen type XI in cho/cho mice (Li et al. 1995) and patients with Stickler syndrome (Vikkula et al. 1995); identical phenotypes of Cbfa1 +/− heterozygous mice (Otto et al. 1997) and patients with cleidocranial dysplasia (Mundlos et al. 1997), which lack the expression of one allele of the Cbfal gene; as well as mice with targeted ablation of the second zinc finger of the vitamin D receptor DNA-binding domain as a model of vitamin D-dependent rickets type II (Li et al. 1997). The latter examples underscore the invaluable importance of transgenic and knock-out animals in skeletal research.