Refinement of the dentinogenesis imperfecta type II locus to an interval of less than 2 centiMorgans at chromosome 4q21 and the creation of a yeast artificial chromosome contig of the critical region.

Dentinogenesis imperfecta type II is an autosomal-dominant disorder of dentin formation which has been mapped to the 6.6 centiMorgan D4S2691-D4S2692 interval at human chromosome 4q21. In the current investigation, the use of four short tandem repeat polymorphisms has allowed the critical region to be refined to an interval of less than 2 centiMorgans defined by recombination events in unrelated, affected individuals from two families both of which show independent evidence for linkage to chromosome 4q21. The creation of a yeast artificial chromosome contig of this newly defined interval has allowed us to demonstrate that the critical region encompasses approximately 2 Mb of DNA and that the dentin-specific gene, dentin sialoprotein, maps to this interval within 300 kb of dentin matrix acidic phosphoprotein 1 and bone sialoprotein. Moreover, dentin sialoprotein shows no recombination with the dentinogenesis imperfecta type II phenotype. Dentin sialoprotein is therefore a candidate for the dentinogenesis imperfecta type II locus.

Elucidation of the sequence and the genomic organization of the human dentin matrix acidic phosphoprotein 1 (DMP1) gene: exclusion of the locus from a causative role in the pathogenesis of dentinogenesis imperfecta type II.

The dentin matrix acidic phosphoprotein 1 (DMP1) gene has been mapped to human chromosome 4q21 and shown to exhibit no recombination with the autosomal dominant disorder of dentin formation, dentinogenesis imperfecta type II. In the current study, sequencing of DMP1 cDNA and genomic clones has indicated that the human gene contains an open reading frame of 1539 bp, which predicts a highly acidic, serine-rich protein of 513 amino acids. Comparison of the human DMP1-coding sequence with that of the rat, mouse, and cow indicated that the predicted protein contains a conserved hydrophobic signal peptide sequence and an Arg-Gly-Asp cell attachment sequence. The gene is encoded by six exons, the splicing phase of which is type 0, the first exon containing solely 5' untranslated sequence. Sequencing of each of the coding exons in individuals affected by dentinogenesis imperfecta type II failed to reveal any disease-specific mutations, suggesting that mutations in DMP1 are not causative of this condition at least in the two families examined in this study.

Mapping of the human dentin matrix acidic phosphoprotein gene (DMP1) to the dentinogenesis imperfecta type II critical region at chromosome 4q21.

Dentinogenesis imperfecta type II (DGI1) is an autosomal dominant disorder of dentin formation, which has been mapped to human chromosome 4q12-q21. The region most likely to contain the DGI1 locus is a 3.2-cM region surrounding the osteopontin (SPP1) locus. Recently, a novel dentin-specific acidic phosphoprotein (dmp1) has been cloned in the rat and mapped to mouse chromosome 5q21. In the current investigation, we have isolated a cosmid containing the human DMP1 gene. The isolation of a short tandem repeat polymorphism at this locus has allowed us to map the DMP1 locus to human chromosome 4q21 and demonstrate that it is tightly linked to DGI1 in two families (Zmax = 11.01, theta = 0.001). The creation of a yeast artificial chromosome contig around SPP1 has further allowed us to demonstrate that DMP1 is located within 150 kb of the bone sialoprotein and 490 kb of the SPP1 loci, respectively. DMP1 is therefore a strong candidate for the DGI1 locus.

Expression analysis, genomic structure, and mapping to 7q31 of the human sperm adhesion molecule gene SPAM1.

During the course of systematic sequence tag analysis of clones isolated from an adult testis cDNA library, clones 296 and 576 were found to detect 71-74% sequence identity to the guinea pig sperm surface protein PH-20. This surface protein is involved in sperm-egg adhesion in the guinea pig. Nucleotide sequence for 1919 bp of human DNA from a series of overlapping cDNA clones isolated from a testis cDNA library confirmed the sequence identity within a 1527-bp open reading frame to be 71-74% to the guinea pig gene and the similarity to be 60% for the predicted protein of 509 amino acids. Southern blot analysis of human genomic DNA and DNA from somatic cell hybrids indicates that the gene (SPAM1) is unique and does not form part of a larger family and that it maps to chromosome 7. Fluorescence in situ hybridization with yeast artificial chromosome (YAC) clones isolated from the CEPH megaYAC library has refined this localization to 7q31. PCR analysis of genomic DNA and YAC clone DNA has shown that the 1919 bp of the gene that has been cloned covers approximately 11 kb of genomic DNA and is encoded by at least 4 exons. Northern analysis of poly(A)+ mRNA from a range of 16 human tissues has demonstrated that expression of the gene as a single 2.4-kb transcript is strictly limited to the testis.

Cloning of the X-linked glycerol kinase deficiency gene and its identification by sequence comparison to the Bacillus subtilis homologue.

cDNA clones from a human adult testis cDNA library were isolated and sequenced as part of a programme to produce expressed sequence tags (ESTs). ESTs were used routinely to search DNA and protein sequence databases. One clone (142) showed 60% identity to the Bacillus subtilis glycerol kinase gene at both the DNA and amino acid sequence levels. Analysis of DNA from somatic cell hybrids carrying deleted X chromosomes, has shown that clone 142 detects homologous sequences between Xp21.2-p22.1 (the interval containing the locus responsible for glycerol kinase deficiency--GKD). These sequences are deleted in two patients with GKD. Clone 142 also detects homologous sequences on Xq and at several autosomal loci. The sequences of clone 142 and two further cDNA clones isolated from a human foetal brain cDNA library are presented.