Familial and individual variation in chromosome fragility

Selection of probes for fluorescence in situ hybridization analysis by differential display polymerase chain reaction of mRNA from rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a malignancy of skeletal muscle derivation encompassing two major subtypes, embryonal and alveolar, which differ in clinical behavior and genetic markers. Because RMS is a relatively circumscribed tumor system for which the beginnings of a molecular genetic framework are in place, it becomes an ideal model for the application of improved methods of molecular genetic analysis. We have applied the technique known as differential display polymerase chain reaction (DD-PCR) to characterize expression of RNA in rhabdomyosarcoma subtypes. Our studies have shown that DD-PCR generates a characteristic electrophoretic profile that can be used to isolate subtype specific probes for fluorescence in situ hybridization (FISH) analysis. We have isolated two cDNA fragments and obtained clones suitable for FISH mapping to metaphase chromosomes. One probe was mapped to the centromeric region of human chromosome 22 and the other probe to the human chromosome band 6q25-26. This approach demonstrates the utility of DD-PCR as a technique for isolating novel cDNA expressed in tumors and their subsequent use as probes for FISH analysis. As more genes are identified by DD-PCR and their roles in tumorigenesis become defined, they are likely to provide novel targets for future molecular cytogenetic analysis.

Effect of radiation and cigarette smoking on expression of FUdR-inducible common fragile sites in human peripheral lymphocytes

In vitro X-irradiation of human peripheral blood lymphocytes increased the frequencies of fluorodeoxyuridine-induced fragile sites in a dose-related manner. However, the cells from 30 atomic bomb survivors exposed to either high or low radiation doses 47 years earlier showed no demonstrable difference in fragile site expression, indicating that fragile site induction was ephemeral in nature. When fragile sites were analyzed on the basis of tobacco smoking habits, an elevated number was observed in the smokers. The results confirm that fragile sites can be affected by recent exposure to exogenous agents, but the effect is probably of limited duration, based on the atomic bomb survivor experience.

Identifying chromosomal fragile sites from individuals: a multinomial statistical model

The inability to identify fragile sites from data for single individuals remains the major obstacle to determining whether these chromosomal loci are predisposed to cancer-causing and evolutionary rearrangements. We describe a novel statistical model that is amenable to data from single individuals and that establishes site-specific chromosomal breakage as nonrandom with respect to the distribution of total breakage. Our method tests incrementally smaller subsets of the data for homogeneity under a multinomial model that assigns equal probabilities to a maximal set of nonfragile sites and unrestricted probabilities to the remaining fragile sites with significantly higher numbers of breaks. We show how standardized Pearson's chi-square (X2) and likelihood-ratio (G2) statistics can be appropriately used to measure goodness-of-fit for sparse contingency (individual-based) data in this model. A sample application of this approach indicates extensive variation in fragile sites among individuals and marked differences in fragile-site inferences from pooled as opposed to per-individual data.