D-type cyclins (cyclins D1, D2, and D3) are key components of cell cycle machinery in mammalian cells. These proteins are believed to drive cell cycle progression by associating with their kinase ...partners, cyclin-dependent kinases, and by directing phosphorylation of critical cellular substrates. In addition, D-cyclins play a kinase-independent role by sequestering cell cycle inhibitors p27Kip1. In the past, we and others generated cyclin D1-deficient mice and have shown that these mice display developmental abnormalities, hypoplastic retinas, and pregnancy-insensitive mammary glands. To test the significance of cyclin D1-p27Kip1interaction within a living mouse, we crossed cyclin D1-deficient mice with mice lacking p27Kip1, and we generated double-mutant cyclin D1-/-p27-/-animals. Here we report that ablation of p27Kip1restores essentially normal development in cyclin D1-deficient mice. Our results provide genetic evidence that p27Kip1functions downstream of cyclin D1.
In this study, we show that two biochemical markers of neuronal ceroid lipofuscinoses (NCLs) are present in a mutant mouse (mnd/mnd) that exhibits symptoms of the disease. Subunit c of the ...mitochondrial F1F0-ATP synthase, a proteolipid that accumulates in storage bodies of most forms of NCL and several animal models, is dramatically increased in mnd/mnd mouse brain, kidney, liver, heart, and pancreas. Interestingly, another related proteolipid, subunit c of the vacuolar H(+)-ATPase, also accumulates in several mnd/mnd tissues. The molar ratio of the vacuolar subunit c to the F1F0 subunit c is approximately one to two in enriched storage bodies from brain. The relative accumulation of the vacuolar subunit c correlates with its abundance in normal tissues. It appears in decreasing amounts in brain, kidney, and liver and is not detected in heart or pancreas. Aged mice and two mutant mouse lines, juvenile bare (jb) and mucopolysaccharidosis, type VII (gusmps), did not accumulate either of these proteolipids. Dolichol-linked oligosaccharides also accumulate in NCLs and are increased 17-fold in mnd/mnd mouse brain. Thus, mnd/mnd mice seem to be an excellent model for NCLs since they not only share clinical signs and histopathology, but also two biochemical markers. The accumulation of the vacuolar subunit c in this model may prove to be a marker for distinguishing different forms of NCLs.
The mouse polyomavirus encodes a tumor-suppressor gene inactivator in its large T protein and a proto-oncogene activator in its middle T protein. We have used site-directed mutagenesis to selectively ...inactivate the former function without affecting the latter. Two mutant viruses were constructed to encode altered large T proteins that fail to bind the retinoblastoma tumor-suppressor gene product pRB, along with normal small and middle T proteins. The pRB-binding mutants proved to be defective in immortalization of primary rat embryo fibroblasts by a variety of tests. Yet they proved capable of transforming both primary and established fibroblasts in culture. Most importantly, the inability of these mutants to bind pRB had little effect on their ability to induce tumors in mice. We conclude that induction of multiple tumor types in this system does not depend on large T-pRB interactions but rather on middle T-dependent pathways. In addition, the ability of this virus to immortalize cells in culture is not essential to its ability to induce tumors in the animal.
Highlights • Mixed chimerism without GVHD across MHC barriers can be achieved in a RIC swine HCT model • Mixed chimeras are highly resistant to delayed DLI GVH effects • Pre-DLI leukodepletion ...overcomes resistance to conversion • GVHD is often, but not always, observed post-DLI conversion
Activating mutations in the
ras oncogene are not considered sufficient to induce abnormal cellular proliferation in the absence of cooperating oncogenes. We demonstrate that the conditional ...expression of an endogenous
K-ras
G12D
allele in murine embryonic fibroblasts causes enhanced proliferation and partial transformation in the absence of further genetic abnormalities. Interestingly,
K-ras
G12D
-expressing fibroblasts demonstrate attenuation and altered regulation of canonical Ras effector signaling pathways. Widespread expression of endogenous
K-ras
G12D
is not tolerated during embryonic development, and directed expression in the lung and GI tract induces preneoplastic epithelial hyperplasias. Our results suggest that endogenous oncogenic
ras is sufficient to initiate transformation by stimulating proliferation, while further genetic lesions may be necessary for progression to frank malignancy.
Common incidental pathologic findings in Old World monkeys are spheroid-like structures and iron pigment in the substantia nigra and globus pallidus. The occurrence of each finding correlates with ...the number of years monkeys have spent in captivity. The spheroids are eosinophilic and argyrophilic, but are generally PAS, iron, and luxol fast blue negative. Ultrastructurally, they consist of aggregations of dense globules and granules interspersed with membranes; normal organelles are absent. One classic spheroid with a thin myelin sheath and accumulated fibrillar material was observed. The material in spheroids is ultrastructurally distinguishable from iron pigment, which is present in glial cells, and from neuronal lipofuscin. Accumulation of spheroids and iron pigmentation may be age-related phenomena involving portions of the brain with shared anatomical and biochemical characteristics. The study of these changes may shed light on the pathogenesis of such spheroid degenerations as Hallervorden-Spatz disease.
Activation of PPARgamma by synthetic ligands, such as thiazolidinediones, stimulates adipogenesis and improves insulin sensitivity. Although thiazolidinediones represent a major therapy for type 2 ...diabetes, conflicting studies showing that these agents can increase or decrease colonic tumors in mice have raised concerns about the role of PPARgamma in colon cancer. To analyze critically the role of this receptor, we have used mice heterozygous for Ppargamma with both chemical and genetic models of this malignancy. Heterozygous loss of PPARgamma causes an increase in beta-catenin levels and a greater incidence of colon cancer when animals are treated with azoxymethane. However, mice with preexisting damage to Apc, a regulator of beta-catenin, develop tumors in a manner insensitive to the status of PPARgamma. These data show that PPARgamma can suppress beta-catenin levels and colon carcinogenesis but only before damage to the APC/beta-catenin pathway. This finding suggests a potentially important use for PPARgamma ligands as chemopreventative agents in colon cancer.
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