We have isolated and partially sequenced the human bone sialoprotein gene (IBSP). IBSP has been sublocalized by in situ hybridization to chromosome 4q28-q31 and is composed of six small exons (51 to 159 bp) and 1 large exon (approximately 2.6 kb). The intron/exon junctions defined by sequence analysis are of class O, retaining an intact coding triplet. Sequence analysis of the 5' upstream region revealed a TATAA (nucleotides -30 to -25 from the transcriptional start point) and a CCAAT (nucleotides -56 to -52) box, both in the reverse orientation. Intron 1 contains interesting structural elements composed of polypyrimidine repeats followed by a poly(AC)n tract. Both types of structural elements have been detected in promoter regions of other genes and have been implicated in transcriptional regulation. Several differences between the previously published cDNA sequence (L. W. Fisher et al., 1990, J. Biol. Chem. 265, 2347-2351) and our sequence have been identified, most of which are contained within the untranslated exon 1. Three base revisions in the coding region include a G to T (Gly to Val, amino acid 195), T to C (Val to Ala, amino acid 268), and T to A (Glu to Asp, amino acid 270). In conclusion, the genomic organization and potential regulatory elements of human IBSP have been elucidated.

A treatment has been developed to alleviate muscle weakness in murine dystrophy. Cultured myoblasts from genetically normal mouse embryos were injected into the right soleus of 20-day-old normal or dystrophic mice. Hosts and donors were immunocompatible but exhibited different genotype markers. Donor cells produced GPl-1CC. Host cells produced GPl-1BB. When compared with contralateral controls 6 months postoperatively, test dystrophic solei exhibited greater cross-sectional area, total fiber number, wet weight, and twitch and tetanus tensions. They contained more normal-appearing and less abnormal-appearing fibers. Their mean fiber resting potential was similar to that of normal controls. Presence of GPl-1CC with or without the hybrid isozyme GPl-lBC in these muscles implied the survival and development of donor myoblasts into normal myofibers, and fusion of normal myoblasts with dystrophic satellite cells to form genetically mosaic myofibers. Injection of fibroblasts instead of myoblasts caused detrimental effects.

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