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Molecular nature of ultraviolet B light-induced deletions in the murine epidermis
M Horiguchi1, K I Masumura, H Ikehata
1Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Abstract:
Depletion of the stratospheric ozone layer leads to an increase in ambient UV loads, which are expected to raise skin cancer incidences. Tumor development in the skin could be a multistep process in which various genetic alterations, such as point mutations and deletions, occur successively. Here, we demonstrate that UVB irradiation efficiently induces deletions in the epidermis using a novel transgenic mouse, gpt delta. In this mouse model, deletions in lambda DNA integrated in the chromosome are preferentially selected as Spi(-) (sensitive to P2 interference) phages, which can then be subjected to molecular analysis. The mice were exposed to UVB at single doses of 0.3, 0.5, 1.0, 1.5, and 2.0 kJ/m(2). After 4 weeks, lambda phage was rescued from the genomic DNA of the epidermis by in vitro packaging reactions. The mutant frequencies of Spi(-) with large deletions in the epidermis increased >15-fold at a UVB dose of 0.5 kJ/m(2) over the control. Molecular sizes of most of the large deletions were >1000 bp. More than one-half of the large deletions occurred between short direct-repeat sequences from 1 to 6 bp, and the remainder had flush ends. In the unirradiated mouse, almost all of the Spi(-) mutants were 1-bp frameshifts in runs of identical bases. These results suggest that UVB irradiation induces deletions in the murine epidermis, and most of the deletions are generated through end-joining of double strand breaks in DNA.
Insights
Ultraviolet B (UVB) radiation significantly increases large DNA deletions in mouse skin, a key step in skin cancer development. This study utilized a novel transgenic mouse model to demonstrate UVB-induced genetic alterations in the epidermis.
Area of Science:
- Genetics and Molecular Biology
- Dermatology and Cancer Research
- Environmental Health and Toxicology
Background:
- Stratospheric ozone depletion elevates ambient ultraviolet (UV) radiation levels.
- Increased UV exposure is linked to higher incidences of skin cancer.
- Skin tumor development is a multistep genetic process involving mutations and deletions.
Purpose of the Study:
- To investigate the induction of DNA deletions in the epidermis by UVB irradiation.
- To quantify UVB-induced deletions using a novel transgenic mouse model.
Main Methods:
- Utilized the gpt delta transgenic mouse model for detecting DNA deletions.
- Exposed mice to single doses of UVB radiation (0.3–2.0 kJ/m²).
- Rescued lambda phage from genomic DNA of the epidermis for molecular analysis of deletions.
Main Results:
- UVB irradiation significantly increased mutant frequencies of large deletions (>1000 bp) in the epidermis by over 15-fold at 0.5 kJ/m².
- Most large deletions occurred between short direct-repeat sequences (1–6 bp).
- Unirradiated mice primarily showed 1-bp frameshift mutations in runs of identical bases.
Conclusions:
- UVB irradiation efficiently induces large DNA deletions in the murine epidermis.
- These deletions are likely generated through the end-joining of DNA double-strand breaks.
- Findings highlight a critical mechanism linking UV exposure to skin cancer initiation.