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Loss of Cdk4 expression causes insulin-deficient diabetes and Cdk4 activation results in beta-islet cell hyperplasia
S G Rane1, P Dubus, R V Mettus
1Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Abstract:
To ascertain the role of cyclin-dependent kinase 4 (Cdk4) in vivo, we have targeted the mouse Cdk4 locus by homologous recombination to generate two strains of mice, one that lacks Cdk4 expression and one that expresses a Cdk4 molecule with an activating mutation. Embryonic fibroblasts proliferate normally in the absence of Cdk4 but have a delayed S phase on re-entry into the cell cycle. Moreover, mice devoid of Cdk4 are viable, but small in size and infertile. These mice also develop insulin-deficient diabetes due to a reduction in beta-islet pancreatic cells. In contrast, mice expressing a mutant Cdk4 that cannot bind the cell-cycle inhibitor P16INK4a display pancreatic hyperplasia due to abnormal proliferation of beta-islet cells. These results establish Cdk4 as an essential regulator of specific cell types.
Insights
Cyclin-dependent kinase 4 (Cdk4) is crucial for mouse development and fertility. Its absence causes reduced pancreatic beta cells and diabetes, while a mutation leads to pancreatic hyperplasia.
Area of Science:
- Cell biology
- Molecular biology
- Genetics
Background:
- Cyclin-dependent kinase 4 (Cdk4) is a key regulator of the cell cycle.
- Its precise in vivo function and role in specific cell types remain incompletely understood.
Purpose of the Study:
- To elucidate the in vivo function of Cdk4.
- To investigate the consequences of Cdk4 deficiency and aberrant activation.
Main Methods:
- Targeted homologous recombination in mice to generate Cdk4-deficient and mutant Cdk4 strains.
- Analysis of embryonic fibroblasts and whole animal phenotypes, including cell cycle progression, size, fertility, and pancreatic islet cell mass.
Main Results:
- Mice lacking Cdk4 are viable but exhibit reduced size, infertility, and insulin-deficient diabetes due to fewer pancreatic beta-islet cells.
- Embryonic fibroblasts lacking Cdk4 show normal proliferation but delayed S phase re-entry.
- Mice expressing a mutant Cdk4 resistant to P16INK4a inhibition display pancreatic hyperplasia from beta-islet cell overproliferation.
Conclusions:
- Cdk4 is essential for normal development, fertility, and the regulation of pancreatic beta-islet cell mass.
- Cdk4 plays a critical role in controlling cell proliferation and differentiation in specific tissues.