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Effects of heterozygosity for the Rb-1t19neo allele in the mouse
D J Harrison1, M L Hooper, J F Armstrong
1Department of Pathology, University Medical School, Edinburgh, UK.
Abstract:
We describe the pathology of a cohort of 80 mice heterozygous for an inactive allele of the Rb-1 tumour suppressor gene. The majority of these mice developed locally invasive tumours, arising from the pituitary gland. The time of onset of overt signs of disease in mice known to have inherited their mutant allele paternally shows a small but statistically significant shift to the lower end of the spectrum, suggesting that tumorigenesis is influenced by gametic imprinting. In situ hybridisation analysis demonstrates the presence in the tumours of pro-opiomelanocortin mRNA, which is normally found both in corticotroph and melanotroph cells. Mice within this cohort also develop systemic defects. Most notably, there is increased siderosis in the spleen indicating the possibility of an abnormality in red blood cell turnover. This is consistent with the abnormalities of erythropoiesis described previously in homozygous Rb-1-deficient mice. In addition, a proportion of mice developed liver steatosis, probably representing the end organ effects of hormonal imbalance as a direct consequence of tumour presence. A significant proportion showed C cell hyperplasia in the thyroid. The spectrum of pathology in mice differs from that in the human but does provide a useful model of site-specific tumour predisposition.
Insights
Mice with a mutated Rb-1 tumor suppressor gene frequently developed pituitary tumors and systemic issues like spleen siderosis. Paternal inheritance of the mutation suggested gametic imprinting influences tumor development.
Area of Science:
- Oncology
- Genetics
- Pathology
Background:
- The Retinoblastoma 1 (Rb-1) gene is a critical tumor suppressor.
- Germline mutations in Rb-1 predispose individuals to various cancers.
- Understanding Rb-1's role in tumorigenesis is crucial for cancer research.
Purpose of the Study:
- To investigate the pathology and tumor development in mice heterozygous for an inactive Rb-1 allele.
- To explore the influence of gametic imprinting on tumor onset.
- To identify systemic defects associated with Rb-1 deficiency.
Main Methods:
- Pathological examination of 80 mice heterozygous for a mutated Rb-1 allele.
- In situ hybridization to detect pro-opiomelanocortin mRNA in tumors.
- Analysis of systemic defects including spleen siderosis, liver steatosis, and thyroid C cell hyperplasia.
Main Results:
- The majority of mice developed locally invasive pituitary tumors.
- Paternal inheritance of the mutant Rb-1 allele showed a statistically significant earlier onset of disease, suggesting gametic imprinting.
- Associated systemic defects included increased spleen siderosis, liver steatosis, and C cell hyperplasia.
Conclusions:
- Heterozygous Rb-1 deficiency in mice leads to pituitary tumors and systemic pathologies.
- Gametic imprinting appears to influence the timing of tumorigenesis.
- This mouse model offers insights into site-specific tumor predisposition, despite differences from human pathology.
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