Down syndrome (DS), a major cause of mental retardation, is characterized by subtle abnormalities of cortical neuroanatomy, neurochemistry and function. Recent work has shown that chromosome band 21q22 is critical for many of the neurological phenotypes of DS. A gene, DSCAM (Down syndrome cell adhesion molecule), has now been isolated from chromosome band 21q22.2-22.3. Homology searches indicate that the putative DSCAM protein is a novel member of the immunoglobulin (Ig) superfamily that represents a new class of neural cell adhesion molecules. The sequence of cDNAs indicates alternative splicing and predicts two protein isoforms, both containing 10 Ig-C2 domains, with nine at the N-terminus and the tenth located between domains 4 and 5 of the following array of six fibronectin III domains, with or without the following transmembrane and intracellular domains. Northern analyses reveals the transcripts of 9.7, 8.5 and 7.6 kb primarily in brain. These transcripts are differentially expressed in substructures of the adult brain. Tissue in situ hybridization analyses of a mouse homolog of the DSCAM gene revealed broad expression within the nervous system at the time of neuronal differentiation in the neural tube, cortex, hippocampus, medulla, spinal cord and most neural crest-derived tissues. Given its location on chromosome 21, its specific expression in the central nervous system and neural crest, and the homologies to molecules involved in neural migration, differentiation, and synaptic function, we propose that DSCAM is involved in neural differentiation and contributes to the central and peripheral nervous system defects in DS.
Bovine bone morphogenetic protein (bBMP) induces differentiation of mesenchymal-type cells into cartilage and bone. bBMP has an apparent Mr of 18,500 ± 500 and represents <0.001% of the wet weight of bone tissue. A Mr 34,000 protein resembling osteonectin is separated by extraction with Triton X-100. A Mr 24,000 protein and about half of a Mr 22,000 protein are disassociated from bBMP by precipitation in 1.5 M guanidine hydrochloride. Aggregates of bBMP and a Mr 14,000 protein are insoluble in aqueous media; the bBMP becomes soluble when the Mr 14,000 protein is disassociated in 6 M urea and removed from the solution by ultrafiltration. Three separate molecular species with apparent Mrs 18,500, 17,500, and 17,000 are eluted at 0.10, 0.15, and 0.20 M phosphate ion concentrations, respectively, from a hydroxy-apatite column. The Mr 18,500 protein has the amino acid composition of acidic polypeptide and includes four halfcystine residues; the pI is 4.9-5.1. The Mr 22,000 component is a chromoprotein resembling ferritin. The NH12-terminal amino acid sequence of the Mr 17,500 protein simulates histone H2B.The Mr 17,000 protein may possess calmodulin activity. Aggregates of the Mr 18,500 and other proteins induce formation of large deposits of bone; the Mr 18,500 protein alone is rapidly absorbed and induces formation of small deposits. None of the other proteins induces bone formation.Under the influence of bone morphogenetic protein (BMP), perivascular mesenchymal-type cells (pericytes) differentiate into cartilage and woven bone. BMP is an acidic polypeptide (1, 2) embedded in a complex assortment of intra-and extracellular protein aggregates derived from dentin (3), bone (4, 5), and osteosarcoma tissues (6-9). We report here on the purification of BMP by means of a combination of differential precipitation, ultrafiltration, and hydroxyapatite chromatography. MATERIALS AND METHODSTen-kilogram batches of 1-year-old steer long bones were obtained from an abattoir. After the epiphyseal ends were cut away with a band saw, the diaphyses were mechanically scraped clean of soft tissues and extensively washed in cold water solution of 3 mM NaN3. The washed bone was frozen in liquid N2, ground in a Wiley mill to a particle size of 1 mm3, defatted in chloroform/methanol (1:1), and again washed in 10 liters of cold water (step 1). The bone particles were demineralized in 0.6 M HCl at 4°C for 48 hr and again extensively rewashed in NaN3 solution (step 2). The demineralized washed bone particles were chemically extracted to remove soluble noncollagenous protein (i.e., sialoproteins, plasma proteins, y-carboxyglutamyl proteins, and phosphoproteins), simultaneously converting the collagen to insoluble bone matrix gelatin (step 3) by previously described procedures (10). Ten kilograms of whole wet bone produced -'1.4 kg of freeze-dried insoluble bone matrix gelatin. The BMP was extracted from the insoluble bone matrix gelatin in an inorganic/organic solvent mixture of 0.5 M CaCl2 in 6 M urea at 28°C for 24 hr containing 10...
Human bone morphogenetic protein (hBMP) was chemically extracted from demineralized gelatinized cortical bone matrix by means of a CaClz urea inorganic-organic solvent mixture, differential precipitation in guanidine hydrochloride, and preparative gel electrophoresis. hBMP is isolated in quantities of 1 mg/kg of wet weight of fresh bone, and has the amino-acid composition of an acidic polypeptide. The mol wt is 17 to 18 k-Da (kilodaltons). Implants of the isolated 17-kDa protein are very rapidly adsorbed and produce a smaller volume of bone than protein fractions consisting of 24-, 17-, and 14-kDa proteins. Since the isolated 24-and 14-kDA components lack hBMP activity, the kinetics of the bone morphogenetic processes including the function of other proteins as camer molecules, await investigation. 194
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