The genomes of various tumour cells contain mutant oncogenes that act dominantly, in that their effects can be observed when they are introduced into non-malignant cells. There is evidence for another class of oncogenes, in which tumour-predisposing mutations are recessive to wild-type alleles. Retinoblastoma is a prototype biological model for the study of such recessive oncogenes. This malignant tumour, which arises in the eyes of children, can be explained as the result of two distinct genetic changes, each causing loss of function of one of the two homologous copies at a single genetic locus, Rb, assigned to the q14 band of human chromosome 13. Mutations affecting this locus may be inherited from a parent, may arise during gametogenesis or may occur somatically. Those who inherit a mutant allele at this locus have a high incidence of non-ocular, second tumours, almost half of which are osteosarcomas believed to be caused by the same mutation. Here we describe the isolation of a complementary DNA segment that detects a chromosomal segment having the properties of the gene at this locus. The gene is expressed in many tumour types, but no RNA transcript has been found in retinoblastomas and osteosarcomas. The cDNA fragment detects a locus spanning at least 70 kilobases (kb) in human chromosome band 13q14, all or part of which is frequently deleted in retinoblastomas and osteosarcomas.

/pdf/a-human-dna-segment-with-properties-of-the-gene-that-kc0q4f65ya.pdf

A human DNA segment with properties of the gene that predisposes to retinoblastoma and osteosarcoma

Inheritance of a mutation at the Rb-1 locus, which has been mapped to band q14 of human chromosome 13, results in predisposition to retinoblastoma. Cloned DNA segments homologous to arbitrary loci of human chromosome 13 and which reveal polymorphic restriction endonuclease recognition sequences, have been used to look for somatic genetic events that might occur during tumorigenesis. A comparison of constitutional and tumour genotypes from several cases indicates that tumorigenesis may result from the development of homozygosity for the mutant allele at the Rb-1 locus. The homozygosity in these cases results from mitotic nondisjunction, resulting in loss of the homologous wild-type chromosome, or from a mitotic recombination event.

Expression of recessive alleles by chromosomal mechanisms in retinoblastoma

https://www.cell.com/cell/pdf/S0092-8674(00)80540-1.pdf

Monoallelically expressed gene related to p53 at 1p36, a region frequently deleted in neuroblastoma and other human cancers.

Recent evidence indicates the existence of a genetic locus in chromosome region 13q14 that confers susceptibility to retinoblastoma, a cancer of the eye in children. A gene encoding a messenger RNA (mRNA) of 4.6 kilobases (kb), located in the proximity of esterase D, was identified as the retinoblastoma susceptibility (RB) gene on the basis of chromosomal location, homozygous deletion, and tumor-specific alterations in expression. Transcription of this gene was abnormal in six of six retinoblastomas examined: in two tumors, RB mRNA was not detectable, while four others expressed variable quantities of RB mRNA with decreased molecular size of about 4.0 kb. In contrast, full-length RB mRNA was present in human fetal retina and placenta, and in other tumors such as neuroblastoma and medulloblastoma. DNA from retinoblastoma cells had a homozygous gene deletion in one case and hemizygous deletion in another case, while the remainder were not grossly different from normal human control DNA. The gene contains at least 12 exons distributed in a region of over 100 kb. Sequence analysis of complementary DNA clones yielded a single long open reading frame that could encode a hypothetical protein of 816 amino acids. A computer-assisted search of a protein sequence database revealed no closely related proteins. Features of the predicted amino acid sequence include potential metal-binding domains similar to those found in nucleic acid-binding proteins. These results provide a framework for further study of recessive genetic mechanisms in human cancers.

https://science.sciencemag.org/content/sci/235/4794/1394.full.pdf

Human retinoblastoma susceptibility gene: cloning, identification, and sequence

Tumor suppressor genes.

Normal melanocytes and melanocytes of normal nevi, primary melanoma in the radial (RGP) and vertical (VGP) growth phases, and metastatic melanoma exhibited and maintained phenotypic differences when grown in tissue culture or in experimental animals. Only metastatic and VGP primary melanoma cells were tumorigenic in athymic nude mice and had nonrandom chromosomal abnormalities involving chromosomes 1, 6, and 7. The colony-forming efficiency in soft agar was also highest in these two cell types. A cell line of RGP primary melanoma had characteristics of both benign and malignant cells: nevus-like morphology; nontumorigenicity in nude mice; but karyotypic abnormality of chromosome 6. It also had a ganglioside pattern similar to that of normal melanocytes but not melanomas, i.e., a high GM3 ganglioside content compared to the amounts of GM2, GD2, and GD3 gangliosides. Binding of monoclonal antibodies secreted by hybridomas generated by immunization of mice with VGP primary and metastatic melanoma was highest with cells and supernatants of cultures from advanced melanoma and least with nevus cells. There was no binding to normal melanocytes except with the monoclonal antibodies specific for nerve growth factor receptor or 9-O-acetyl-GD3 ganglioside. On the other hand, monoclonal anti-nevus antibodies bound to melanocytes, nevus cells, and RGP primary melanoma cells but not to VGP primary or metastatic melanoma cells. Cultured human melanocytic cells appear to be a unique model for the study of tumor progression.

https://cancerres.aacrjournals.org/content/canres/45/11_Part_2/5670.full.pdf

Characteristics of Cultured Human Melanocytes Isolated from Different Stages of Tumor Progression

Structural rearrangements of chromosome 1p have been reported previously as a frequent finding in human neuroblastomas. In a review of karyotypes from 35 neuroblastomas (including 29 published cases and 6 unpublished tumors and cell lines), it was found that, in addition to the abnormalities of chromosome 1p (found in approximately 70% of cases), abnormalities involving only 2 other chromosome segments occurred with significant frequency (in 20% or more of cases) in this cancer. These abnormalities involved trisomies for the long arms of chromosomes 1 and 17. In addition, two novel cytogenetic aberrations, homogeneously staining regions and double minutes, were identified in two-thirds of the cases. It is postulated that the gene change(s) produced by the abnormalities of chromosome 1p in neuroblastoma play a primary role in the development of this cancer. The gene changes produced by the abnormalities of chromosomes 1q and 17q and by the homogeneously staining regions and double minutes are presumed to contribute to tumor progression.

/pdf/human-neuroblastomas-and-abnormalities-of-chromosomes-1-and-3lon54vfry.pdf

Human neuroblastomas and abnormalities of chromosomes 1 and 17.

Cytogenetics of human malignant melanoma and premalignant lesions

Epidermal growth factor (EGF) receptor is expressed selectively by human melanoma cells which show the presence of an extra copy of chromosome 7. None of the cells of benign pigmented lesions (nevi) or radial growth phase (nonmetastatic) primary melanoma expressed EGF receptor and none of these cells showed an extra copy of chromosome 7. The results indicate that a single extra dose of a gene (for EGF receptor) may provide a selective advantage to cells in the late stages of tumorigenesis.

Gloria Balaban

Papers

Characteristics of Cultured Human Melanocytes Isolated from Different Stages of Tumor Progression

Human neuroblastomas and abnormalities of chromosomes 1 and 17.

Cytogenetics of human malignant melanoma and premalignant lesions

Expression of the receptor for epidermal growth factor correlates with increased dosage of chromosome 7 in malignant melanoma.

Karyotypic evolution in human malignant melanoma.