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Induction of somatic intrachromosomal recombination inversion events by cyclophosphamide in a transgenic mouse model
P J Sykes1, A M Hooker, C S Harrington
1Department of Haematology, Flinders University of South Australia, Bedford Park, Australia. pam.sykes@flinders.edu.au
Abstract:
Somatic intrachromosomal recombination (SICR) can result in chromosomal inversion and deletion, mechanisms which are important in carcinogenesis. We have utilised a transgenic mouse model to study SICR inversion events in spleen cells. The transgenic construct is designed so that expression of an Escherichia coli lacZ transgene only occurs in a cell when an SICR inversion event occurs in the region of the transgene. The inversion events can then be detected by histochemical staining of frozen spleen sections for transgene expression and by polymerase chain reaction across the inversion breakpoints. The spontaneous inversion frequency in spleen rose 2-fold from 1.54 +/- 0.24 x 10(-4) (mean +/- SE) in 4-month-old transgenic mice to 3.12 +/- 0.67 x 10(-4) in 22-month-old mice. Four- or 8-month-old mice were treated with a single intraperitoneal injection of cyclophosphamide, with doses ranging from 0.01 to 100 mg/kg. The animals were killed 3 days after treatment. A significant induction of SICR inversions was detected at all doses with a 3.2-fold maximum induction of inversions detected at 10 mg/kg. These results suggest that the transgenic mouse model used here may be a sensitive model for studying the role of SICR in mutation and in studying risk assessment of environmental DNA-damaging agents.
Insights
Somatic intrachromosomal recombination (SICR) causes DNA mutations like inversions, crucial in cancer development. A new mouse model effectively detects these SICR events, aiding in assessing environmental DNA-damaging agents.
Area of Science:
- Genetics
- Molecular Biology
- Carcinogenesis
Background:
- Somatic intrachromosomal recombination (SICR) is a mechanism leading to chromosomal inversions and deletions, implicated in cancer.
- Understanding SICR is vital for assessing DNA damage and cancer risk.
Purpose of the Study:
- To develop and utilize a transgenic mouse model for studying SICR inversion events in spleen cells.
- To investigate the spontaneous frequency of SICR inversions with age.
- To evaluate the genotoxic potential of cyclophosphamide using this model.
Main Methods:
- A transgenic mouse model was engineered where lacZ transgene expression indicates SICR inversion.
- Inversion events were detected via histochemical staining of spleen sections and PCR across breakpoints.
- Mice of different ages were treated with cyclophosphamide, and spleen sections analyzed for SICR induction.
Main Results:
- Spontaneous SICR inversion frequency in spleen cells doubled between 4 and 22 months of age.
- Cyclophosphamide treatment significantly induced SICR inversions across all tested doses.
- A maximum 3.2-fold induction of inversions was observed at a cyclophosphamide dose of 10 mg/kg.
Conclusions:
- The developed transgenic mouse model is sensitive for studying SICR-mediated mutations.
- This model shows promise for the risk assessment of environmental DNA-damaging agents.