Detection of somatic mutations in tumours of diverse types by DNA fingerprinting with M13 phage DNA

Application of inter-simple sequence repeat PCR to mouse models: assessment of genetic alterations in carcinogenesis

Genomic instability is believed to play a significant role in cancer development by facilitating tumor progression and tumor heterogeneity. Inter-simple sequence repeat (inter-SSR) PCR has been proved to be a fast and reproducible technique for quantitation of genomic instability (amplifications, deletions, translocations, and insertions) in human sporadic tumors. However, the use of inter-SSR PCR in animal models of cancer has never been described. This new technique has been adapted in our laboratory for the analysis of spontaneous and induced mouse tumors. We established the best PCR conditions for each microsatellite-anchored primer and critically evaluated the reproducibility of the band patterns. We also studied the variation of the fingerprints between and within various inbred mouse strains, including wild-derived lines. Tumor-specific alterations were detected as gains, losses, or intensity changes in bands when compared with matched normal DNA. We quantitated the extent of alterations by dividing the number of altered bands in the tumor by the total number of bands in normal DNA (instability index). By means of inter-SSR PCR, we successfully analyzed genomic alterations in various mouse tumors, including spontaneous thymic lymphomas developed in Msh2 knockout mice as well as chemically induced squamous cell carcinomas and thymic lymphomas. Instability index values ranged between 0 and 9%, the highest levels observed in N-methyl-N-nitrosourea-induced thymic lymphomas generated in Trp53 (p53) nullizygote (-/-) mice. We report here, for the first time, the use of inter-SSR PCR to detect somatic mutations in mouse tumoral DNA, including laser-capture microdissected, methanol-fixed tissues. These PCR-based fingerprints provide a novel approach to assessing the number and onset of mutational events in mouse tumors and will help to understand better the mechanisms of carcinogenesis in mouse models.

Merkel cell carcinoma. Histopathology, immunohistochemistry, and cytogenetic analysis

BACKGROUND

Merkel cell carcinoma (MCC) is a cutaneous neoplasm, histopathologically difficult to differentiate from other small blue cell neoplasms. Immunohistochemical and ultrastructural analyses are usually helpful in differentiating these neoplasms. Recently, cytogenetic analysis has emerged as a potential tool in the diagnosis of solid neoplasms, including MCC.

OBJECTIVE

To describe the immunohistochemical and cytogenetic features of a case of primary MCC and to review the cytogenetics literature on MCC.

METHODS

Formalin-fixed tissue was processed routinely and labeled with a battery of antibodies. Metaphase cells from fresh tissue were prepared by Giemsa banding.

RESULTS

Histopathologically, there were irregular aggregates of pyknotic cells with little cytoplasm. Immunohistochemically, the neoplastic cells stained positive for neurofilament, cytokeratin, neuron-specific enolase, and epithelial membrane antigen. Leucocyte common antigen, S-100, 013, and chromogranin were negative. Karyotyping of neoplastic cells showed loss of chromosome Y (-Y).

CONCLUSIONS

Coexpression of cytokeratin and neurofilament is characteristic of MCC and allows it to be differentiated from similar neoplasms. The significance of Y chromosome loss is unclear. Further cytogenetic analyses are warranted to identify genetic mutations significant to the pathogenesis of MCC.

Detection of a progression-linked DNA restriction fragment in rat hepatoma cells probed with a hexokinase cDNA

We have compared genomic DNA isolated from a series of rat hepatomas and from normal rat liver tissue by restriction fragment analysis. Our objective was to identify a tumor-specific restriction fragment that would be present in rapidly growing tumors and missing in normal tissues. Using a cDNA probe specific for the C-terminal half of rat brain hexokinase, we have identified several changes in DNA restriction fragment lengths in rat hepatomas vs. normal rat liver. Most of these involved restriction fragments that were present in normal rat DNA and missing in tumor DNA. However, one HinfI fragment of M(r) = 13.4 kilobase pairs (kb) was found to be present in rapidly growing rat hepatomas, but missing in normal rat tissue and in hepatomas of slow or intermediate growth rate.

Improved resolution and sensitivity of human DNA fingerprinting by specific-primed labelling of M13 DNA

A method to label M13 DNA probe by primer extension using a specific oligonucleotide primer is described. The method specifically labels the two 15-bp repeats in M13 DNA which hybridize to target DNA giving rise to DNA fingerprinting patterns. The M13 probe labelled by this method gave superior DNA fingerprinting patterns that that labelled by random primers. As little as 0.25 microgram of target DNA was sufficient for DNA fingerprinting. Non-isotopic labelling by the specific primer also showed improved DNA fingerprinting pattern. The results demonstrate the methodology to improve DNA fingerprinting based on M13 DNA probe.

Detection of somatic DNA alterations in ovarian cancer by DNA fingerprint analysis

The M13 phage single-strand DNA probe which recognizes highly polymorphic loci was applied to HinfI-digested DNA isolated from tumor tissue and peripheral leukocytes from 20 patients with ovarian cancer. An average of 22 minisatellite-containing DNA fragments were observed per individual. DNA fingerprint analysis revealed a change in restriction-fragment-length patterns in the DNA from 12 of 20 (60%) tumors compared with the patient's constitutional DNA. Deletion of one or more bands from the tumor was recognized by the probe in seven cases, new bands were identified in two, and intensity shift was demonstrated in eight. The authors conclude that the unmapped M13 minisatellite probe is a useful method for identifying cancer-related somatic DNA alterations.

Detection of genomic alterations in carcinogen-induced mouse liver tumors by DNA fingerprint analysis

DNA fingerprint analysis was used to study structural abnormalities in the genome of mouse liver tumor cells. Liver tumors were induced in three strains of mice, namely C57BL/6J, C3H/He and B6C3F1, by a single injection of 20 micrograms/g body wt. diethylnitrosamine on day 15 after birth. DNA from liver tumors was digested with Hinfl restriction enzyme and hybridized on Southern blots with wild-type bacteriophage M13 DNA as probe. The resulting fingerprints of tumor DNA were compared with those of DNA from normal liver tissue. Genomic aberrations were detected in two out of 68 tumors analyzed, one stemming from a C57BL/6J and the other from a C3H/He mouse.