Mice lacking cyclin D1 have been generated by gene-targeting in embryonic stem cells. Cyclin D1-deficient animals develop to term but show reduced body size, reduced viability, and symptoms of neurological impairment. Their retinas display a striking reduction in cell number due to proliferative failure during embryonic development. In situ hybridization studies of normal mouse embryos revealed an extremely high level of cyclin D1 in the retina, suggesting a special dependence of this tissue on cyclin D1. In adult mutant females, the breast epithelial compartment fails to undergo the massive proliferative changes associated with pregnancy despite normal levels of ovarian steroid hormones. Thus, steroid-induced proliferation of mammary epithelium during pregnancy appears to be driven through cyclin D1.
LP. Sicinski, J. Liu Donaher, S. B. Parker, T. Li, A. Fazeli, H. Gardner, S. Z. Haslam, R. S. Bronson, S.J. Elledge, R.A. Weinberg: Cyclin D1 provides a link between development and oncogenesis in the retina and breast. Cell 82, 621-630 (1995) (Abstract).
Background
Cyclin D1 is a critical component of the cell cycle clock apparatus. Aberrant expression
of this protein has been documented in the variety of human malignancies. Most striking is
the involvement of this cyclin in human breast cancer. In order to better understand the
role played by this cyclin in the proliferation and differentiation of various cell types,
we have applied the technique of gene targeting through homologous recombination in
embryonic stem (ES) cells created mice lacking cyclin D1.
Gene Targeting Vector
The targeting vector deletes coding portions of exons I-III of the cyclin D1 gene and
replaces them with the neomycin resistance gene.
Mouse Strains
TheD1-/- mutation was established in C57/BL6x129/Sv mixed genetic background.
Homozygous mutant D1-/- females that survived until adulthood passed through sexual maturation. The breast tissue of these mice was able to achieve a fully developed state as judged by both histologic and whole-mount analysis A dramatic anomaly in mammary function first became manifest after D1-/- females delivered pups. These females were unable to nurse, because of a defect in pregnancy-associated mammary tissue proliferation. Specifically, these mutant D1-/- glands displayed a dramatic impairment in the expansion of mammary epithelium. In particular, the development of alveolar lobules that usually occurs during pregnancy was virtually absent in the mutant mice. The number of side-branches clearly increased during the pregnancy of the mutant mice and small clusters of alveoli were formed but the overall rate of expansion was inconsequential when compared with the pregnancy-associated epithelial proliferation seen in the mammary glands of wild-type mice. On the other hand, cyclin D1 -/- females displayed normal levels of ovarian steroids in their blood and normal levels of estrogen receptors in mammary epithelium.
Future Directions
We have also generated mouse knockouts of two cell cycle proteins-(cyclin D2 and D3) that
are highly homologous to cyclin D1. We are currently analyzing their phenotype.
Key Words
D-cyclins, gene targeting, mammary proliferation
Submitted by
Peter Sicinski on February 8, 1996
Whitehead Institute
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email sicinski@wi.mit.edu
contributed March 1996
last update: December 1998