Expression of alpha-D-mannosidase in man-hamster somatic cell hybrids

Isolation and characterization of the gene encoding the mouse broad specificity lysosomal alpha-mannosidase1

A genomic clone encoding the mouse lysosomal alpha-mannosidases was isolated and the gene was found to be encoded by 24 exons spanning approximately 14.5 kb of genomic DNA. The intron-exon boundaries were conserved between the mouse, human, and bovine lysosomal alpha-mannosidase genes as well as being partially conserved in several other species. In order to define the promoter of the mouse mannosidase gene, >1 kb of DNA sequence was obtained upstream from the respective initiation codon. The transcription start site was identified by a 5'-RACE procedure and putative promoter elements were identified by expression of promoter/reporter constructs. Fluorescence in situ hybridization analysis using the mouse and human mannosidase genomic clones as probes, localized the mouse gene to chromosome 8, at band position 8C2, and the human gene to chromosome 19p13.2, a region syntenic to the lysosomal mannosidase gene on mouse chromosome 8.

Cloning, expression, purification, and characterization of the human broad specificity lysosomal acid alpha-mannosidase

We have cloned and expressed two cDNAs encoding the human lysosomal alpha-mannosidase (EC 3.2.1.24) by RT-PCR of human spleen mRNA. This enzyme is required for the degradation of N-linked carbohydrates during glycoprotein catabolism in eucaryotic cells. The shorter of the two cDNAs (3 kilobases (kb)) was found to encode an open reading frame of 2964 base pairs and, when expressed in Pichia pastoris, was found to encode an enzyme that could cleave high mannose oligosaccharides, oligosaccharides isolated from alpha-mannosidosis fibroblasts, and p-nitrophenyl-alpha-D-mannopyranoside substrates. In addition, the Pichia-expressed enzyme was inhibited by swainsonine, and had a pH optimum, Km, and Vmax characteristic of the enzyme purified previously from human liver. The second, larger RT-PCR product (3.6 kb) was found to contain an insertion and a deletion relative to the 3-kb spleen amplimer and encoded a truncated coding region, indicating that it resulted from alternate transcript splicing. No alpha-mannosidase activity could be detected in Pichia transformants containing this coding region, indicating that it did not encode a functional enzyme. Antiserum raised to the recombinant product of the 3-kb alpha-mannosidase cDNA immunoprecipitated lysosomal alpha-mannosidase activity from human fibroblast extracts. Northern blots identified a 3-kb RNA transcript in all human tissues tested, including alpha-mannosidosis fibroblasts, while minor transcripts of 3.6 kb were also present in several adult tissues. Human chromosome mapping of the mannosidase gene confirmed that the functional gene maps to the MANB locus on chromosome 19. Sequence comparisons were made to previously published human cDNA sequences encoding a putative lysosomal alpha-mannosidase (Nebes, V. L., and Schmidt, M. C. (1994) Biochem. Biophys. Res. Commun. 200, 239-245) and several differences were found relative to the functional lysosomal alpha-mannosidase encoded by the 3-kb spleen cDNA.

Gene mapping of ocular diseases

Increasing awareness of the role of genetic factors in the causation of many human eye diseases has made ocular genetics one of the fastest growing areas of ophthalmology. The objective of this paper is to present the basic principles of gene mapping and their application to ophthalmology. The techniques used to map the genome are reviewed with emphasis placed on molecular genetics. The advances in this area have already provided the major impetus to the areas of diagnosis and prevention of some genetic eye disorders. Tables are presented that list the autosomal, X-linked and mitochondrial assignment of eye genes and disorders with ocular involvement.

Localization of the malignant hyperthermia susceptibility locus to human chromosome 19q12-13.2

Malignant hyperthermia (MH) is an inherited human skeletal muscle disorder and is one of the main causes of death due to anaesthesia. The reported incidence of MH varies from 1 in 12,000 in children to 1 in 40,000 in adults. MH is triggered in susceptible people by all commonly used inhalational anaesthetics; it is characterized by a profoundly accelerated muscle metabolism, contractures, hyperthermia and tachycardia. Susceptibility to MH (MHS) is predicted by contracture tests on muscle tissue obtained by biopsy. An almost identical disorder known as porcine MH exists in pigs. The genetics of the porcine syndrome have been extensively studied; the locus controlling expression of porcine MH is genetically linked to the glucose phosphate isomerase locus (GPI). In man, GPI has been mapped to the q12-13.2 region of chromosome 19 (refs 10-12). We have now investigated genetic linkage in several extended Irish pedigrees in which MHS is segregating as an autosomal dominant trait. Here we show linkage between MHS and DNA markers from the GPI region of human chromosome 19 with a maximum log likelihood ratio (lod score) of 5.65 at the CYP2A locus. These results indicate that human and porcine MH are most probably due to mutations in homologous genes, and also provide a potentially accurate and noninvasive method of diagnosis for MHS.

Further regional localization of the genes for human acid alpha glucosidase (GAA), peptidase D (PEPD), and alpha mannosidase B (MANB) by somatic cell hybridization

We have further regionally localized the gene for human acid alpha glucosidase (GAA) to 17q21----q23 by examination of hybrid clones derived from a fusion between human fibroblasts carrying a 17/19 balanced translocation (17pter----17q23::19p13.3----19pter; 19qter----p13.3::17q23----17qter) and a mouse line deficient in thymidine kinase. These hybrids were constantly maintained in HAT selective media in order to select for the presence of the human thymidine kinase gene on the intact chromosome 17 (17q21-q22) or the 17/19 (17pter----17q23::19p13.3----19pter) translocation chromosome. We detected human GAA by rocket immunoelectrophoresis, using a human specific heterologous antibody raised against human acid alpha glucosidase (GAA) (Honig et al. 1984). Three secondary clones, which contained the 17/19 translocation and no intact chromosome 17 or 19, were still positive for GAA. Two of these secondary clones contained the distal portion of the 17/19 translocation chromosome, with a break in the band 17q21 (probably at 17q21.2), attached to a mouse chromosome. Combined with earlier results (Weil et al. 1979; Nickel et al. 1982; Honig et al. 1984), the gene for GAA can be assigned to 17q21.2----17q23. Additionally, these clones were negative for human peptidase D (PEPD), alpha mannosidase B (MANB), and phosphohexose isomerase (PHI). Combined with previous results (Ingram et al. 1977; Bruns et al. 1979), these results exclude the genes for PEPD and MANB from 19pter----19p13.3 and confirm the exclusion of the gene for PHI from this segment of chromosome 19 (Wilson et al. 1984; Ingram et al. 1977).

Localisation of genetic markers and orientation of the linkage group on chromosome 19

A panel of human-rodent somatic cell hybrids containing translocation derivatives of human chromosome 19 has been used to assign the markers peptidase D, complement component 3, lysosomal mannosidase, lysosomal DNAase, chorionic gonadotropin beta-subunit, and a new polymorphic DNA sequence, to specific regions of chromosome 19. This has allowed the relative orientations of the genetic and physical maps to be established, and provides the framework for a search for the genes responsible for inherited disorders on chromosome 19, such as myotonic dystrophy and neurofibromatosis.

Isolation and sequence of a human apolipoprotein CII cDNA clone and its use to isolate and map to human chromosome 19 the gene for apolipoprotein CII

cDNA clones encoding human apolipoprotein CII (apo CII) were identified by screening an adult human liver cDNA library with a mixed oligonucleotide probe corresponding to all possible codons for apo CII amino acid 6-10. One clone with an approximately equal to 500-base-pair (bp) insert, designated pCII -711, was selected for DNA sequence analysis. This clone contained a DNA sequence that corresponded with the previously reported amino acid sequence of apo CII with only minor differences. The DNA sequence specified a polypeptide of 79 amino acids, compared to the 78 amino acids previously reported. The pCII -711 clone contains a 36-bp DNA sequence upstream from that specifying the NH2-terminal threonine which, when read in frame, specifies the amino acid sequence Leu-Val-Leu-Leu-Val-Leu-Gly-Phe-Glu-Val-Gln-Gly and may be part of an apo CII signal peptide. The pCII -711 clone also contains a 144-bp region that corresponds to the 3' untranslated region of apo CII mRNA as well as a portion of the poly(A) tail. Clone pCII -711 was used to isolate and characterize by restriction endonuclease digestion the gene for apo CII from a human genomic library. In addition, through Southern blot analysis of DNA from human-rodent somatic cell hybrids, clone pCII -711 also was used to provisionally map the gene for apo CII to human chromosome 19.

Assignment of the human gene for peptidase E to the chromosomal region 17q23----17qter

Peptidase E has been studied in 16 independent human-Syrian hamster hybrids and 16 subclones. Evidence is presented indicating that the human gene for Peptidase E is on chromosome 17 in the region 17q23----17qter.

Genetic variation for prolidase (PEP-4) in the mouse maps near the gene for glucosephosphate isomerase (GPI-1) on chromosome 7

An inherited electrophoretic variant of prolidase (EC 3.4.13.9), also called peptidase 4 (PEP-4), has been discovered among inbred strains of mice. Analysis of progeny from reciprocal backcrosses established that the electrophoretic forms are expressed codominantly and that Pep-4 is located between the genes for glucosephosphate isomerase (Gpi-1) and pink-eyed dilution (p) on chromosome 7. These data define a region of conserved gene linkage between mouse chromosome 7 and human chromosome 19, as originally indicated by somatic cell hybrid studies, and imply that human prolidase (PEPD) is located in the region of human chromosome 19 pter greater than q13.

Human lysosomal genes: arylsulfatase A and beta-galactosidase

The segregation of human lysosomal arylsulfatase A (ARS-A) has been evaluated in 50 primary hybrid clones derived from four separate fusions involving WBCs from two unrelated individuals and three hamster cell lines. ARS-A was expressed in the hybrids as a dimeric molecule of very similar or identical subunits. The expression of this enzyme was concordant with that of mitochondrial aconitase (ACON-M), an isozyme assigned to chromosome 22, in all 50 clones and with chromosome 22 segregation in all but one of the 29 karyotyped hybrids. No other human chromosome cosegregated with 22 in these clones, suggesting that this enzyme is specified in hybrid cells by a locus (or loci) on a single chromosome. beta-Galactosidase (B-GAL) expression was analyzed with two different electrophoresis systems and with a number of cell extract preparation methods in 39 of the primary hybrid clones. The B-GAL isozyme expressed in these hybrid cells was concordant with the expression of glutathione peroxidase-1 (GPX-1), an isozyme assigned to chromosome 3, in all 39 clones and with the segregation of this chromosome in 97% of the 29 karyotyped hybrids. These observations substantiate the prior tentative assignments of an ARS-A locus to chromosome 22 and a B-GAL locus to chromosome 3 (Bruns et al., 1978a, b). The implications of the chromosome assignments of loci for 12 human lysosomal enzymes for the cellular assembly of these organelles are discussed.