The genomic structure of the gene defective in Usher syndrome type Ib (MYO7A).

Usher syndrome type Ib is a recessive autosomal disorder manifested by congenital deafness, vestibular dysfunction, and progressive retinal degeneration. Mutations in the human myosin VIIa gene (MYO7A) have been reported to cause Usher type Ib. Here we report the genomic organization of MYO7A. An STS content map was determined to discover the YAC clones that would cover the critical region for Usher syndrome type Ib. Three of the YACs (802A5, 966D6, and 965F10) were subcloned into cosmids and used to assemble a preliminary cosmid contig of the critical region. Part of the gene encoding human myosin VIIa was found in the preliminary cosmid contig. A cosmid, P1, PAC, and long PCR contig that contained the entire MYO7A gene was assembled. Primers were designed from the composite cDNA sequence and used to detect intron-exon junctions by directly sequencing cosmid, P1, PAC, and genomic PCR DNA. Alternatively spliced products were transcribed from the MYO7A gene: the largest transcript (7.4 kb) contains 49 exons. The MYO7A gene is relatively large, spanning approximately 120 kb of genomic DNA on chromosome 11q13.

Immunohistochemical localization of basement membrane collagens and associated proteins in the murine cochlea.

Immunohistochemistry using antibodies specific for each of the basement membrane collagen chains was used to assess the location and composition of basement membranes in the mouse cochlea. The classical chains (COL4A1, 4A2) localized primarily in the osseous spiral lamina and in the capillaries of the spiral ligament. In contrast, the novel collagen chains (4A3, 4A4, and 4A5) localized to the interdental cells of the sulcus, the inner sulcus, the basilar membrane, and the region of type II fibrocytes in the spiral ligament. Antibodies against type 4A5 collagen also heavily stained the stria vascularis. Weak staining in the stria was observed with antibodies against 4A3. Basement membrane-associated proteins were also assessed. The basement membrane in the perineurium of the osseous spiral lamina immunostained using antibodies against laminin, heparan sulfate proteoglycan, and entactin. The basilar membrane contained only fibronectin in association with the novel collagen chains. The capillaries of the spiral ligament and the stria vascularis stained heavily for heparin sulfate proteoglycan and laminin. Generalized staining for laminin was observed in the spiral ligament. These results indicate that an abundance of basement membrane collagen containing extracellular matrix exists in the murine cochlea and that the composition of these matrices are surprisingly varied and tissue specific.

Narrowing the genetic interval and yeast artificial chromosome map in the branchio-oto-renal region on chromosome 8q.

Branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder characterized by branchial abnormality, hearing loss, and renal anomalies. Recently, the disease gene has been localized to chromosome 8q. Here, we report genetic studies that further refine the disease gene region to a smaller interval and identify several YACs from the critical region. We studied two large, clinically well-characterized BOR families with a set of 13 polymorphic markers spanning the D8S165-D8S275 interval from the chromosome 8q region. Based on multipoint analysis, the highest likelihood for the location of the BOR gene is between markers D8S543 and D8S530, a distance of about 2 cM. YACs that map in the BOR critical region have been identified and characterized by fluorescence in situ hybridization and pulsed-field gel electrophoresis. A YAC contig, based on the STS content map, that covers a minimum of 4 Mb of human DNA in the critical region of BOR is assembled. This lays the groundwork for the construction of a transcriptional map of this region and the eventual identification of genes involved in BOR syndrome.