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Identification of mutations in the Ki-ras gene in human retinoblastoma
D Bautista1, J R Emanuel, C Granville
1Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520-8023, USA.
Purpose:
To investigate the mutational status of the Ki-ras gene in retinoblastoma and to evaluate a correlation of the genotype with clinical and histopathologic variables.
Methods:
Tumor samples were microdissected from sectioned archival paraffin-embedded tissue. Ki-ras genomic sequences (exons 1 and 2) were amplified by polymerase chain reaction then analyzed by single-strand conformation polymorphism and direct sequencing. Tissue sections, flanking the analyzed samples, were stained with hematoxylin and eosin for examination by light microscopy.
Results:
Four of 12 tumors had mutation in exon 1, codon 12 of the Ki-ras gene; none had mutation in exon 2. Signal intensity of the mutated alleles indicates clonal mutation in the tumor cell populations. One of four bilateral tumors was mutated, and all three samples with undifferentiated histologic appearance harbored a clonal Ki-ras mutation. However, only one of nine moderately to poorly differentiated tumors harbored a mutation.
Conclusions:
Ki-ras, an oncogene seldom altered in neuroectodermal neoplasms, is mutated in one third of the retinoblastomas studied. The Ki-ras mutations are clonal, suggesting that affected cells have a selective growth advantage. The mutations are present and are likely to play a pathogenetic role in heritable and sporadic retinoblastomas. These results suggest that mutations in Ki-ras are preferentially associated with undifferentiated tumors.
Insights
Ki-ras gene mutations were found in one-third of retinoblastoma tumors studied. These clonal mutations, particularly in undifferentiated tumors, suggest a role in the disease's development.
Area of Science:
- Oncology
- Genetics
- Ophthalmology
Background:
- Retinoblastoma is a pediatric eye cancer.
- The role of oncogene mutations in retinoblastoma is not fully understood.
Purpose of the Study:
- Investigate Ki-ras gene mutations in retinoblastoma.
- Correlate Ki-ras genotype with clinical and histopathologic features.
Main Methods:
- Microdissection of archival paraffin-embedded tumor tissues.
- Polymerase chain reaction amplification of Ki-ras exons 1 and 2.
- Single-strand conformation polymorphism and direct sequencing for mutation analysis.
Main Results:
- Ki-ras mutations identified in 4 of 12 (33.3%) retinoblastoma tumors, exclusively in exon 1, codon 12.
- Clonal Ki-ras mutations were detected in tumor cell populations.
- Mutations were more frequent in undifferentiated tumors (3/3) compared to differentiated ones (1/9).
Conclusions:
- Ki-ras oncogene mutations occur in a significant subset of retinoblastomas.
- Clonal Ki-ras mutations suggest a selective growth advantage for affected cells.
- These mutations may play a pathogenetic role in both heritable and sporadic retinoblastomas, particularly in undifferentiated tumors.