T. Mohandas

Human and mouse amelogenin gene loci are on the sex chromosomes

Enamel is the outermost covering of teeth and is the hardest tissue in the vertebrate body. The enamel matrix is composed of enamelin and amelogenin classes of protein. We have determined the chromosomal locations for the human and mouse amelogenin (AMEL) loci using Southern blot analyses of DNA from human, mouse, or somatic cell hybrids by hybridization to a characterized mouse amelogenin cDNA. We have determined that human AMEL sequences are located on the distal short arm of the X chromosome in the p22.1----p22.3 region and near the centromere on the Y chromosome, possibly at the proximal long arm (Yq11) region. These chromosomal assignments are consistent with the hypothesis that perturbation of the amelogenin gene is involved in X-linked types of amelogenesis imperfecta, as well as with the Y-chromosomal locations for genes that participate in regulating tooth size and shape. Unlike the locus in humans, the mouse AMEL locus appears to be assigned solely to the X chromosome. Finally, together with the data on other X and Y chromosome sequences, these data for AMEL mapping support the notion of a pericentric inversion occurring in the human Y chromosome during primate evolution.

Cloning and expression of steroid sulfatase cDNA and the frequent occurrence of deletions in STS deficiency: Implications for X-Y interchange

Human STS is a microsomal enzyme important in steroid metabolism. The gene encoding STS is pseudoautosomal in the mouse but not in humans, and escapes X inactivation in both species. We have prepared monoclonal and polyclonal antibodies to the protein which has been purified and from which partial amino acid sequence data have been obtained. cDNA clones containing the entire coding sequence were isolated, sequenced, and expressed in heterologous cells. Variable length transcripts have been shown to be present and due to usage of alternative poly(A) addition sites. The functional gene maps to Xp22.3-Xpter and there is a pseudogene on Yq suggesting a recent pericentric inversion. Absence of STS enzymatic activity occurs frequently in human populations and produces a visible phenotype of scaly skin or ichthyosis. Ten patients with inherited STS deficiency were studied and eight had complete gene deletions. The possibility that STS deficiency results from aberrant X-Y interchange is discussed.

A detailed genetic map of the long arm of chromosome 11

We describe 14 new restriction fragment length polymorphisms, corresponding to 13 loci on the long arm of chromosome 11. A detailed genetic map of chromosome 11q has been constructed from these and other loci (a total of 31 loci) typed in 59 reference families. The 23 most informative markers were selected to establish a map with a strongly supported order; regional localizations are provided for eight other markers. The loci span 88 cM in males and 148 cM in females and form a dense continuum on 11q. These ordered polymorphic markers will be of help in studying the genes responsible for several diseases that have been localized to this region, including genes responsible for multiple endocrine neoplasia type I (MEN1), ataxia telangiectasia (AT), tuberous sclerosis (TSC), and some forms of asthma and rhinitis.

Directed isolation of human genes that escape X inactivation

Existing methodologies have been combined to produce a directed approach to the isolation of human genes that escape X inactivation. A mouse-human somatic cell hybrid line was established that has an inactive X as its only human chromosome, and nuclear RNA from this cell line was used to construct a cDNA library. Transcribed human sequences were isolated by screening the library with labeled human DNA. The corresponding genomic sequences were isolated in phage or cosmid clones, and exons were identified by detection of transcripts on northern blots. By these means three human loci have been identified that contain genes expressed from an inactive X chromosome. Fluorescence in situ hybridization has been used to map these genes to Xp21.1–22.1, Xp22.1–22.2, and terminal Xp/Yp. One of the three genes (XE45) corresponds to the ZFX gene, while the other two genes (XE7 and XE59) represent novel cloned sequences. Physical and genetic evidence indicate that XE7 is a newly identified pseudoautosomal gene.

Localization of monocyte chemotactic protein-1 gene (SCYA2) to human chromosome 17q11.2–q21.1

Monocyte chemotactic protein-1 (MCP-1) is a member of the small inducible gene (SIG) family. It has been shown to play a role in the recruitment of monocytes to sites of injury and infection. By analysis of a panel of somatic cell hybrids, we have localized the MCP-1 gene, designated SCYA2, to human chromosome 17. In situ hybridization confirmed this assignment and further localized the gene to 17q11.2-q21.1.

A primary map of 24 loci on human chromosome 16

A primary genetic map of chromosome 16 has been constructed by linkage analysis of 24 polymorphic loci, typed in 59 reference families. These loci form a continuous map that covers the whole chromosome and spans genetic distances of 187 cM in males and 226 cM in females. Most of the sex-specific recombination rate difference comes from a nontelomeric region that covers 10 cM in males and 74 cM in females. Both telomeric regions show the opposite trend, with a significant increase in the male recombination rate.

Assignment of the human gene for cholesteryl ester transfer protein to chromosome 16q12–16q21

We have used a cDNA probe for human cholesteryl ester transfer protein (CETP) to determine the chromosomal location for the human gene. Southern blot analysis of DNA from 17 independent mouse-human somatic cell hybrids demonstrated the presence of the gene for human CETP on chromosome 16. Regional mapping of the gene by in situ hybridization was consistent with these results and indicated that the gene resides in the 16q12-21 region of the chromosome. These findings provide an additional polymorphic marker for chromosome 16, as several relatively common restriction fragment length polymorphisms of the gene have previously been reported, and they have significance for studies directed at the identification of genetic factors affecting plasma lipoprotein metabolism and atherosclerosis.

Human pepsinogen C (progastricsin) polymorphism: Evidence for a single locus located at 6p21.1-pter ☆ ☆☆

A series of six clones containing the entire human pepsinogen C gene (PGC) was identified in a cosmid vector library by using cDNA and oligonucleotide probes. The 10.7-kb PGC gene includes nine exons and exhibits a high degree of sequence identity (60%) with the functionally related pepsinogen A genes. The predicted amino acid sequence was identical with the partial amino-terminal and carboxyl-terminal sequences of purified pepsinogen C. An informative restriction fragment length polymorphism was detected with several restriction enzymes and involved an insertion or deletion of 100 bp of intron sequence located between exons 7 and 8. Evidence that there is only a single PGC gene in humans is presented. The PGC gene and the prolactin gene were regionally localized to 6p21.1-pter by analysis of mouse X human somatic cell hybrids.

Assignment of human pancreatic lipase gene (PNLIP) to chromosome 10q24-q26

Human pancreatic lipase (EC 3.1.1.3) is a 56-kDa protein secreted by the acinar pancreas and is essential for the hydrolysis and absorption of long-chain triglyceride fatty acids in the intestine. In vivo, the 12-kDa protein cofactor, colipase, is required to anchor lipase to the surface of lipid micelles, counteracting the destabilizing influence of bile salts. Southern blot analysis, using a pancreatic lipase cDNA to probe DNA from mouse-human somatic cell hybrids, indicated that the pancreatic lipase gene (PNLIP) resides on human chromosome 10. In situ hybridization to human metaphase chromosomes confirmed the cell hybrid results and further localized the gene to the 10q24-qter region with the strongest peak at q26.1.

Dispersed family of human genes with sequence similarity to farnesyl pyrophosphate synthetase

Prenyltransferases are a group of enzymes involved in the biosynthesis of both sterol and nonsterol isoprene compounds. Somatic cell hybrid studies and in situ hybridization show that the human genome contains five distinct loci that hybridize to the cDNA for the enzyme farnesyl pyrophosphate synthetase (FPS), a prenyltransferase that catalyzes the synthesis of an intermediate common to both the sterol and the nonsterol branches of the isoprene biosynthetic pathway. The loci identified in this report may correspond to unique prenyltransferase genes related to FPS or to pseudogenes. The loci mapped have been identified as farnesyl pyrophosphate synthetase-like-1 (FPSL-1) on chromosome 1q24-31, FPSL-2 on chromosome 7, FPSL-3 on chromosome 14, FPSL-4 on chromosome 15q14-q21, and FPSL-5 on chromosome Xq21-22. Multiple copies of sequences similar to those of FPS are also present in both the mouse and the rat.