ISOLATION OF MARKERS FOR CHONDRO-OSTEOGENIC DIFFERENTIATION USING CDNA LIBRARY SUBTRACTION - MOLECULAR-CLONING AND CHARACTERIZATION OF A GENE BELONGING TO A NOVEL MULTIGENE FAMILY OF INTEGRAL MEMBRANE-PROTEINS

To identify novel marker molecules associated with chondro-osteogenic differentiation, we have set up a differential screening system based on a cDNA library subtraction in organ cultures of prenatal mouse mand ibular condyles, Differential screening of a cDNA library constructed from in vitro cultured condyles allowed the isolation of a novel gene, named E25, Full-length E25 cDNA is predicted to encode a type II inte gral membrane protein of 263 amino acid residues, In situ hybridizatio n experiments show that E25 is expressed in the outer perichondrial ri m of the postnatal mandibular condyle, which contains the proliferatin g progenitor cells, but not in the deeper layers of the condyle contai ning the more differentiated chondroblasts and chondrocytes, Other car tilagenous tissues and their perichondrium were negative, Strong in si tu hybridization signals were also detected on bone trabeculae of matu re bone in tooth germs and in hair follicles, Northern blot analysis s howed strong expression in osteogenic tissues, such as neonatal mouse calvaria, paws, tail, and in skin, This expression profile suggests th at E25 could be a useful marker for chondro-osteogenic differentiation . Homology searches of DNA databanks showed that E25 belongs to a nove l multigene family, containing three members both in man and mouse. Th e mouse E25 gene locus (Itm2) was mapped to the X chromosome.