Molecular detection of deletions involving band q14 of chromosome 13 in retinoblastomas.

Abstract

DNA fragments from a locus spanning 29 kilobases within chromosome band 13q14 detected deletions in 3 retinoblastomas out of 37 such tumors examined. Somatically occurring, homozygous deletions spanning at least 25 kilobases were detected in retinoblastomas from two unrelated patients. These deletions are bounded by the esterase D locus proximally. In a third patient, both tumor cells and leukocytes have a deletion of one chromosome 13 homolog, with one end of the deletion localized to a 1.55-kilobase fragment within the cloned region. It is likely that the cloned locus is within a few hundred kilobases of the retinoblastoma gene (i.e., the locus governing predisposition to such tumors) and that the deletions detected also involve the retinoblastoma gene. Further, it may be possible to base a successful approach to the isolation of the retinoblastoma gene on this assumed physical proximity of the two loci.It has been about 80 years since the appearance of published reports of families in which a parent who was cured of retinoblastoma had children afflicted with the same type of tumor (ref. 1, p. 336; ref. 2). There is evidence from more recent studies that the heritability of predisposition to retinoblastoma is governed by a locus within human chromosome band 13q14 (3-8). Furthermore, the locus is representative of a class of such loci in the human genome, called recessive oncogenes (9, 10). The loci are related, since it appears that recessive, mutant alleles at any of the loci tend to be oncogenic and, correspondingly, that the dominant alleles normally present at the loci have a role in preventing tumor formation (11)(12)(13)(14)(15)(16). The evidence supporting this genetic nature of alleles at the retinoblastoma locus has been indirect; i.e., the locus has not been isolated for direct molecular study.A proportion of the recessive mutations at the locus that predispose to tumor formation are deletions (3,4 MATERIALS AND METHODSOrigin of Probes. There are three loci established to be within 13q14: the esterase D locus and the loci detected by probes pH3-8 and pH2-42 (4, 17). Probes pH3-8 and pH2-42 were derived from a phage library enriched for DNA sequences from chromosome 13 by using a fluorescenceactivated chromosome sorter (17). Esterase D is an enzyme, of unknown biologic function, that demonstrates allelic isozymes (18). One other locus, named 7D2, is closely linked to the esterase D locus and is probably within or near 13q14 (19).Other probes that detect loci assigned to chromosome 13 and were used in this study are p7F12, p9D11, plE8, p9A7, pHU10, pHU26, and pHUB8 (20,21). The sublocalization of the loci detected by these probes has been determined by deletion mapping (20,21) and by in situ hybridization (22). Probe p4-A detects an arbitrary autosomal locus not on chromosome 13.Construction of Phage Library. For the purpose of "chromosome walking," a total human phage library was constructed. Normal human lymphoblast DNA was digested partially with Mbo I, with due regard to the calculations ...

Patterns of risk of hereditary retinoblastoma and applications to genetic counselling

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Mouse mammary tumor virus/v-Ha- ras transgene-induced mammary tumors exhibit strain-specific allelic loss on mouse chromosome 4

“…Allele-specific LOH is often found in tumors associated with familial cancer syndromes, at the site of the responsible gene (1-3, 8, 9). Delineating the boundaries of a minimal region of common LOH among multiple tumors has been a useful approach in positional cloning of candidate novel tumor suppressor genes (1,2,(10)(11)(12).…”

Molecular biology of prostate cancer

“…If one copy of the gene is already missing because of an inherited defect, then loss of the sole remaining allele results in complete absence of that gene's product, which can lead to a cancer. The loss of both alleles of a gene, termed the 'two-hit' hypothesis by Knudson in 1971, 77 explained the epidemiology of retinoblastoma and loss of the RB gene was later confirmed to be causative [79][80][81][82] (Tables 3 and 4).…”