MOLECULAR GENETICS OF BMP2 AND 4--FOP CANDIDATE GENES

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The embryogenesis and regeneration of the skeleton are complex developmental events dependent on the successful induction of endochondral osteogenesis. Little is known, however, about the genetic control of bone induction. cDNAs have recently been cloned for seven bone morphogenetic proteins (BMP1-7), six of which (BMP2-7) are members of an ancient and highly conserved family of molecules involved in the developmental regulation of embryonic pattern formation. Proteins expressed from two related recombinant clones (BMP2 & 4) possess the capacity to induce the entire developmental program of endochondral osteogenesis in an ectopic site in a pattern histologically identical to that seen in the extremely rare genetic disorder Fibrodysplasia Ossificans Progressiva (FOP). FOP is a progressively disabling connective tissue disorder characterized by congenital malformations of the blastemal anlage of the toes and disordered temporal and spatial induction of endochondral osteogenesis at ectopic sites. Two related hypotheses that provide the focus for our long-term goals are proposed: first, the molecular structure and function of the human BMP2 & 4 genes will provide fundamental insight into the genetic regulation of endochondral bone induction and pattern formation in humans; second, BMP2 & 4 are candidate genes for FOP, and the molecular structure of the regulatory control regions of these genes may be abnormal in patients with FOP. To address these hypotheses, we intend to: 1. Isolate genomic clones for BMP2 & 4 using partial length cDNAs as probes. 2. Identify the transcription initiation sites of BMP2 and BMP4 to define the RNA-coding regions of these genes. 3. Characterize the promoter and other cis- regulatory regions of BMP2 & 4 by DNA sequence analysis. 4. Define the functional control unit of BMP2 & 4 in a promoter/enhancer expression assay system. 5. Perform mutational screening of FOP DNA by RFLP analysis for additions, deletions, or rearrangements in BMP2 & 4 genes using genomic probes (obtained in 1). Analysis of the molecular organization and regulatory control of the human BMP2 & 4 genes will foster the long-term goals of elucidating basic mechanisms of normal and disordered bone induction, and of designing rational molecular diagnostic and treatment strategies for a wide range of developmental disorders of the skeleton in humans.