Germ-line chromosomal localization of human C-Erb-A oncogene

µ-Crystallin: A thyroid hormone binding protein

µ-Crystallin is a NADPH-regulated thyroid hormone binding protein encoded by the CRYM gene in humans. It is primarily expressed in the brain, muscle, prostate, and kidney, where it binds thyroid hormones, which regulate metabolism and thermogenesis. It also acts as a ketimine reductase in the lysine degradation pathway when it is not bound to thyroid hormone. Mutations in CRYM can result in non-syndromic deafness, while its aberrant expression, predominantly in the brain but also in other tissues, has been associated with psychiatric, neuromuscular, and inflammatory diseases. CRYM expression is highly variable in human skeletal muscle, with 15% of individuals expressing ≥13 fold more CRYM mRNA than the median level. Ablation of the Crym gene in murine models results in the hypertrophy of fast twitch muscle fibers and an increase in fat mass of mice fed a high fat diet. Overexpression of Crym in mice causes a shift in energy utilization away from glycolysis towards an increase in the catabolism of fat via β-oxidation, with commensurate changes of metabolically involved transcripts and proteins. The history, attributes, functions, and diseases associated with CRYM, an important modulator of metabolism, are reviewed.

Molecular genetic analysis of recessive mutations at a heterozygous autosomal locus in human cells

We have investigated the genotypic changes that lead to expression of a recessive allele at a heterozygous autosomal locus in a human cell line. Mutant clones lacking thymidine kinase activity were derived from a B-cell lymphoblastoid line initially heterozygous at the tk locus, and restriction mapping was performed to detect intragenic structural alterations in the tk gene. In addition, informative molecular markers located elsewhere on chromosome 17 were analysed in order to detect large-scale (multilocus) events. We report that among 325 spontaneous and induced mutants, allele loss was more common than intragenic rearrangements or point mutations; in many cases, loss of heterozygosity appears to have extended well beyond the locus under selection. Cytogenetic analysis of a subset of these mutants showed that expression of the recessive TK-deficient phenotype and the associated loss of heterozygosity for chromosome 17 markers was not typically associated with detectable chromosomal changes.

Stability of phenotypic and genotypic traits during the establishment of a human neuroblastoma cell line, IGR-N-835

A prerequisite for the study of biological characteristics in neuroblastoma is the establishment of cell lines from tumors of patients. For our study a neuroblastoma cell line, IGR-N-835, was established from a primary tumor. During in vitro establishment of this line morphological changes were observed. IGR-N-835 exhibited both anchored cells and floating clusters. When cultured on bovine endothelial corneal cellular matrix, all tumor cells anchored to the matrix and proliferated, giving a continuous cell line. IGR-N-835 was studied in vitro and in vivo. Treatment with retinoic acid resulted in cell growth arrest and morphological differentiation. IGR-N-835 was highly tumorigenic in nude mice, exhibited a doubling time of 65 hr and was able to form colonies in methyl-cellulose with a cloning efficiency of 0.46%. Immunocytochemical studies showed reactivity of this line and its primary passages with CE7 monoclonal antibody (MAb). Cytogenetic analyses revealed stable mode and markers resulting from structural changes in chromosomes 10, 11 and 21 with no homogeneously staining regions or double minute chromosomes. Genomic amplification and overexpression of the N-myc oncogene exhibited by the patient's tumor remained unchanged in nude mouse xenografts and the IGR-N-835 cell line. These phenotypic and genotypic traits were unchanged during establishment of this neuroblastoma line. IGR-N-835 could therefore constitute a suitable material for the study of the biology or therapeutics of human neuroblastoma.

Molecular characterization of thymidine kinase mutants of human cells induced by densely ionizing radiation

In order to characterize the nature of mutants induced by densely ionizing radiations at an autosomal locus, we have isolated a series of 99 thymidine kinase (tk) mutants of human TK6 lymphoblastoid cells irradiated with either fast neutrons or accelerated argon ions. Individual mutant clones were examined for alterations in their restriction fragment pattern after hybridization with a human cDNA probe for tk. A restriction fragment length polymorphism (RFLP) allowed identification of the active tk allele. Among the neutron-induced mutants, 34/52 exhibited loss of the previously active allele while 6/52 exhibited intragenic rearrangements. Among the argon-induced mutants 27/46 exhibited allele loss and 10/46 showed rearrangements within the tk locus. The remaining mutants had restriction patterns indistinguishable from the TK6 parent. Each of the mutant clones was further examined for structural alterations within the c-erbA1 locus which has been localized to chromosome 17q11-q22, at some unknown distance from the human tk locus at chromosome 17q21-q22. A substantial proportion (54%) of tk mutants induced by densely ionizing radiation showed loss of the c-erb locus on the homologous chromosome, suggesting that the mutations involve large-scale genetic changes.

The cytogenetics of childhood leukemia: clinical and biologic implications

Cytogenetic studies have revealed a broad spectrum of abnormalities in the chromosomal make-up of human leukemic cells. These abnormalities are acquired during the process of malignant transformation within the neoplastic clone and reflect the genetic lesions and ablations that have occurred. Because cytogenetic abnormalities are tightly linked to the molecular events that lead to leukemogenesis, it is not surprising that these features correlate with immunophenotypic and morphologic features of the leukemic cells, as well as with the clinical characteristics of children at diagnosis and their responsiveness to therapy. Molecular analysis of the disordered structure or disrupted regulation of genes located at critical chromosomal breakpoints in leukemic cells should continue to provide important insight into normal and aberrant hematopoietic cell function.

Identification of a novel thyroid hormone receptor expressed in the mammalian central nervous system

A complementary DNA clone derived from rat brain messenger RNA has been isolated on the basis of homology to the human thyroid hormone receptor gene. Expression of this complementary DNA produces a high-affinity binding protein for thyroid hormones. Sequence analysis and the mapping of this gene to a distinct human genetic locus indicate the existence of multiple human thyroid hormone receptors. Messenger RNA from this gene is expressed in a tissue-specific fashion with highest levels in the central nervous system.

Germ-line chromosomal localization of genes in chromosome 11p linkage: parathyroid hormone, beta-globin, c-Ha-ras-1, and insulin

The chromosomal localization of genes for parathyroid hormone (PTH), beta-globin cluster, c-Ha-ras-1, and insulin, all of which have previously been assigned to the short arm of chromosome 11, generated considerable interest because of their association with development of disease states. Furthermore, the availability of recombination data from family studies made the determination of their physical location on the chromosome necessary. Several investigators have attempted this; however, controversy has arisen concerning the location of beta-globin, insulin, and c-Ha-ras-1 genes. Thus, while the results of some investigators suggested that all three genes are situated in the 11p15 region, data of other investigators placed the beta-globin and insulin genes close to the centromere and c-Ha-ras-1 in a more proximal region than 11p15. The subchromosomal position of the PTH gene remains to be determined. We have performed in situ hybridization of meiotic pachytene bivalents with 3H-labeled cloned genomic probes of PTH, beta-globin, and insulin genes and find their germ-line positions to be the following: PTH at 11p11.21, beta-globin at 11p11.22, and insulin at 11p14.1. These data, when considered with our recent germ-line assignment of the c-Ha-ras-1 gene to 11p14.1, indicate the following relative order on 11p: cen-PTH-beta-globin-c-Ha-ras-insulin or cen-PTH-beta-globin-insulin-c-Ha-ras. The former order is consistent with genetic evidence from linkage analysis of DNA polymorphisms adjacent to these genes segregating in families.

Constitutive fragile sites and cancer

Breaks were observed at 51 sites in homologous chromosomes in lymphocytes from ten humans and two great apes when cells were deprived of thymidine. The incidence of breaks was enhanced by caffeine, a substance that inhibits DNA repair in replicating cells. The locations of 20 sites were correlated with breakpoints that have been related to human malignancy.