The structure and expression of the human neuroligin-3 gene.

The neuroligins are a family of proteins that are thought to mediate cell to cell interactions between neurons. During the sequencing at an Xq13 locus associated with a mental retardation syndrome in some studies, we discovered a portion of the human orthologue of the rat neuroligin-3 gene. We now report the structure and the expression of that gene. The gene spans approximately 30kb and contains eight exons. Unlike the rat gene, it codes for at least two mRNAs and at least one of which is expressed outside the CNS. Interestingly, the putative promoter for the gene overlaps the last exon of the neighboring HOPA gene and is located less than 1kb from an OPA element in which a polymorphism associated with mental retardation is found. These findings suggest a possible role for the neuroligin gene in mental retardation and that the role of the gene in humans may differ from its role in rats.

Identification of three additional genes contiguous to the glucocerebrosidase locus on chromosome 1q21: implications for Gaucher disease.

Gaucher disease results from the deficiency of the lysosomal enzyme glucocerebrosidase (EC 3.2.1.45). Although the functional gene for glucocerebrosidase (GBA) and its pseudogene (psGBA), located in close proximity on chromosome 1q21, have been studied extensively, the flanking sequence has not been well characterized. The recent identification of human metaxin (MTX) immediately downstream of psGBA prompted a closer analysis of the sequence of the entire region surrounding the GBA gene. We now report the genomic DNA sequence and organization of a 75-kb region around GBA, including the duplicated region containing GBA and MTX. The origin and endpoints of the duplication leading to the pseudogenes for GBA and MTX are now clearly established. We also have identified three new genes within the 32 kb of sequence upstream to GBA, all of which are transcribed in the same direction as GBA. Of these three genes, the gene most distal to GBA is a protein kinase (clk2). The second gene, propin1, has a 1.5-kb cDNA and shares homology to a rat secretory carrier membrane protein 37 (SCAMP37). Finally, cote1, a gene of unknown function lies most proximal to GBA. The possible contributions of these closely arrayed genes to the more atypical presentations of Gaucher disease is now under investigation.

The genomic structure and developmental expression patterns of the human OPA-containing gene (HOPA).

We determined the genomic organization of the human OPA-containing gene (HOPA) and characterized its developmental expression. The gene encoding HOPA, which contains a rare polymorphism tightly associated with non-specific mental retardation, is 25 kb in length and consists of 44 exons. A promoter scan analysis demonstrates two possible transcription initiation sites without TATA boxes upstream from the putative translation initiation start site. Several informative polymorphisms are evident in the sequence including a large pentanucleotide repeat. Northern blot analysis of the gene transcript and its murine orthologue, MOPA-1, demonstrates that only one transcript is expressed throughout the soma and the CNS, and that the transcript is highly expressed during early fetal development. We conclude that the delineation of the function of the HOPA gene locus merits further study.

Isolation and characterization of the human tyrosine hydroxylase gene: identification of 5' alternative splice sites responsible for multiple mRNAs.

A full-length genomic clone for human tyrosine hydroxylase (L-tyrosine, tetrahydropteridine:oxygen oxidoreductase, EC 1.14.16.2) has been isolated. A human brain genomic library constructed in EMBL3 was screened by using a rat cDNA for tyrosine hydroxylase as a probe [Brown, E. R., Coker, G. T., III, & O'Malley, K. L. (1987) Biochemistry 26, 5208-5212]. Out of one million recombinant phage, one clone was identified that hybridized to both 5' and 3' rat cDNA probes. Restriction endonuclease mapping. Southern blotting, and sequence analysis revealed that, like its rodent counterpart, the human gene is single copy, contains 13 primary exons, and spans approximately 8 kilobases (kb). In contrast to the rat gene, human tyrosine hydroxylase undergoes alternative RNA processing within intron 1, generating at least three distinct mRNAs. A comparison of the human tyrosine hydroxylase and phenylalanine hydroxylase [DiLella, A. G., Kwok, S. C. M., Ledley, F. D., Marvit, J., & Woo, S. L. C. (1986) Biochemistry 25, 743-749] genes indicates that although both probably evolved from a common ancestral gene, major changes in the size of introns have occurred since their divergence.

Two novel polymorphic sequences in the glucocerebrosidase gene region enhance mutational screening and founder effect studies of patients with Gaucher disease.

Gaucher disease, an inherited glycolipid storage disorder, is caused by a deficiency of the catabolic enzyme glucocerebrosidase (EC 3.2.1.45). The gene for human glucocerebrosidase is located on chromosome 1q21 and has a highly homologous pseudogene situated 16 kb downstream. We report two novel polymorphic sequences in the glucocerebrosidase gene region: the first consists of a variable number of dinucleotide (CT) repeats located 3.2 kb upstream from the glucocerebrosidase gene, and the second is a tetranucleotide (AAAT) repeat found between the glucocerebrosidase gene and its pseudogene, 9.8 kb downstream from the functional gene. These polymorphic sequences, along with a previously reported PvuII polymorphism in intron 6 of the glucocerebrosidase gene, were analyzed in patients with Gaucher disease (n=106) and in two normal control populations, one of Ashkenazi Jewish ancestry (n=72) and the second comprising non-Jewish individuals (n=46). In these samples, strong linkage disequilibrium was found between mutations N370S, c.84-85insG, and R463C and specific haplotypes; no significant linkage disequilibrium was found when examining haplotypes of patients with the L444P mutation. Studies of these polymorphic sites in several instances also led to the recognition of genotyping errors and the identification of unusual recombinant alleles. These new polymorphic sites provide additional tools for mutational screening and founder effect studies of Gaucher disease.