A highly polymorphic region 3′ to the human Type II collagen gene

The antigenic group (Ag) system of homospecific human serum antigens of low density lipoprotein is detected by antiserum from multiply transfused patients. A complex series of common Ag alleles has been described, but the biochemical nature of this polymorphism is uncertain. Here we report that DNA polymorphisms at the human apolipoprotein B (apoB) locus are very closely linked to alleles of the Ag system. We also show a strong association between Ag(x) and a polymorphism detected with the restriction endonuclease Xba I. We conclude that the immunologically determined Ag system represents protein polymorphism of apoB rather than primary genetic differences in posttranslational processing or lipid binding. These studies therefore demonstrate that the Ag locus is located on the short arm of human chromosome 2 in the region p23-p24 to which the apoB gene has been assigned. Since the Ag(x) antigen is associated with altered plasma lipid levels, this determinant may indicate a functionally important domain of apoB.Epidemiological studies have shown a strong correlation between high plasma low density lipoprotein (LDL) cholesterol levels and premature coronary heart disease. Plasma LDL is responsible for the transport of cholesterol between peripheral tissues and the liver. LDL concentration is regulated by its rate of production from very low density lipoprotein and clearance by the hepatic LDL receptor. The sole protein component of LDL is apolipoprotein B (apoB), which is essential for the structural integrity ofthe particle and is the ligand that mediates its clearance by the LDL receptor pathway (1-3).The antigenic group (Ag) system of homospecific human serum alloantigens was detected in 1961 by the use of an antiserum from a multiply transfused patient (4). Subsequently, the Ag system was shown to reside in LDL and a complex series of alleles has since been described (5). These variants have been shown to behave as autosomal dominant or codominant traits in families and to have differences in gene frequency between populations. Linkage between the Ag system and other genetic markers has not been demonstrated and the biochemical nature of this polymorphism has not been elucidated (6). It is not known, therefore, whether the Ag antigenic determinants reside in apoB, the carbohydrate side chains of apoB, or in LDL lipid. Homospecific polymorphism of LDL has also been found in most animal species that have been studied and appears to be a ubiquitous phenomenon (6).Plasma LDL concentration is profoundly affected by hereditary factors. Thus defects of the LDL receptor gene cause familial hypercholesterolemia with a marked increase in LDL and severe premature atherosclerosis (1, 2).

Section: Methodssupporting

confidence: 77%

Genetic linkage between the antigenic group (Ag) variation and the apolipoprotein B gene: assignment of the Ag locus.

Berg¹,

Powell²,

Wallis³

et al. 1986

“…Several VNTR or minisatellite sequences have been identified in introns or flanking regions of genes, although no function or consistent structural relationship has been identified. These include the insulin gene (21), HRAS oncogene (22), type II collagen gene (23), and five minisatellite sequences in the vicinity of the a-globin gene cluster at the 16p telomere (24).…”

Section: Discussionmentioning

confidence: 99%

Molecular dissection of a contiguous gene syndrome: frequent submicroscopic deletions, evolutionarily conserved sequences, and a hypomethylated "island" in the Miller-Dieker chromosome region.

Ledbetter

vanTuinen

et al. 1989

The Miller-Dieker syndrome (MDS), composed of characteristic facial abnormalities and a severe neuronal migration disorder affecting the cerebral cortex, is caused by visible or submicroscopic deletions of chromosome band 17pl3. Twelve anonymous DNA markers were tested against a panel of somatic cell hybrids containing 17p deletions from seven MDS patients. All patients, including three with normal karyotypes, are deleted for a variable set of 5-12 markers. Two highly polymorphic VNTR (variable number of tandem repeats) probes, YNZ22 and YNH37, are codeleted in all patients tested and make molecular diagnosis for this disorder feasible. By pulsed-field gel electrophoresis, YNZ22 and YNH37 were shown to be within 30 kilobases (kb) of each other. Cosmid clones containing both VNTR sequences were identified, and restriction mapping showed them to be <15 kb apart. Three overlapping cosmids spanning >100 kb were completely deleted in all patients, providing a minimum estimate of the size of the MDS critical region. A hypomethylated island and evolutionarily conserved sequences were identified within this 100-kb region, indications of the presence of one or more expressed sequences potentially involved in the pathophysiology of this disorder. The conserved sequences were mapped to mouse chromosome 11 by using mouse-rat somatic cell hybrids, extending the remarkable homology between human chromosome 17 and mouse chromosome 11 by 30 centimorgans, into the 17p telomere region.

“…3A). The size of the protected fragment indicates that neither of the consensus poly(A) signals (AATAAA) at 195 and 1389 bases from the stop codon (197) is being used (17). Possible alternative sites could be an ATTAAA sequence at 415 bases or ATTTTTT-AAA at 395 bases (18,19).…”

Section: Methodsmentioning

confidence: 99%

Tissue-specific expression of the human type II collagen gene in mice.

Lovell-Badge¹,

Bygrave²,

Bradley³

et al. 1987

Type II collagen is crucial to the development of form in vertebrates as it is the major protein of cartilage. To study the factors regulating its expression we introduced a cosmid containing the human type II collagen gene, including 4.5 kilobases of 5' and 2.2 kilobases of 3' flanking DNA, into embryonic stem cells in vitro. The transformed cells contribute to all tissues in chimeric mice allowing the expression of the exogenous gene to be studied in vivo. Human type II collagen mRNA is restricted to tissues showing transcription from the endogenous gene and human type II collagen is found in extracellular matrix surrounding chondrocytes in cartilage. The results indicate that the cis-acting requirements for correct temporal and spatial regulation of the gene are contained within the introduced DNA.