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Dyggve--Melchior--Clausen syndrome and Smith-McCort dysplasia are recessive spondyloepimetaphyseal dysplasias caused by loss-of-function mutations in dymeclin (Dym), a gene with previously unknown function. Here we report that Dym-deficient mice display defects in endochondral bone formation similar to that of Dyggve--Melchior--Clausen syndrome and Smith-McCort dysplasia, demonstrating functional conservation between the two species. Dym-mutant cells display multiple defects in vesicle traffic, as evidenced by enhanced dispersal of Golgi markers in interphase cells, delayed Golgi reassembly after brefeldin A treatment, delayed retrograde traffic of an endoplasmic reticulum-targeted Shiga toxin B subunit, and altered furin trafficking; and the Dym protein associates with multiple cellular proteins involved in vesicular traffic. These results establish dymeclin as a novel protein involved in Golgi organization and intracellular vesicle traffic and clarify the molecular basis for chondrodysplasia in mice and men. bone formation | gene trap mutation | Golgi | proteomics | growth plate

Widespread losses of heterozygosity (LOH) in human cancer have been thought to result from chromosomal instability caused by mutations affecting DNA repair/genome maintenance. However, the origin of LOH in most tumors is unknown. The present study examined the ability of carcinogenic agents to induce LOH at 53 sites throughout the genome of normal diploid mouse ES cells. Brief exposures to nontoxic levels of methylnitrosourea, diepoxybutane, mitomycin C, hydroxyurea, doxorubicin, and UV light stimulated LOH at all loci at frequencies ranging from 1-8 x [10.sup.-3] per cell (10-123 times higher than in untreated cells). This greatly exceeds the frequencies at which these agents have been reported to induce point mutations and is comparable to the rates of LOH observed in ES cells lacking the gene responsible for Bloom syndrome, an inherited DNA repair defect that results in greatly increased risk of cancer. These results suggest that LOH contributes significantly to the carcinogenicity of a variety of mutagens and raises the possibility that genome-wide LOH observed in some human cancers may reflect prior exposure to genotoxic agents rather than a state of chromosomal instability during the carcinogenic process. Finally, as a practical matter, chemically induced LOH is expected to enhance the recovery of homozygous recessive mutants from phenotype-based genetic screens in mammalian cells. cancer etiology | cancer genetics | carcinogenesis | genome stability

Mice with H2-Ma mutant genes were developed to study the importance of H2-M in loading peptides onto major histocompatibility complex (MHC) class II molecules. Cells from these mice did not produce complete protein antigens for MHC class II-restricted T cells and were hampered in producing exogenous peptides. The quantity of mature CD4+ T lymphocytes in the mutant mice were only 25 to 33% of the quantity in normal mice.

The therapeutic responsiveness of genetically defined tumors expressing or devoid of the p53 tumor suppressor gene was compared in immunocompromised mice. Tumors expressing the p53 gene contained a high proportion of apoptotic cells and typically regressed after treatment with gamma radiation or adriamycin. In contrast, p53-deficient tumors treated with the same regimens continued to enlarge and contained few apoptotic cells. Acquired mutations in p53 were associated with both treatment resistance and relapse in p53-expressing tumors. These results establish that defects in apoptosis, here caused by the inactivation of p53, can produce treatment-resistant tumors and suggest that p53 status may be an important determinant of tumor response to therapy., Although the tumor-specific action of most anticancer agents has been attributed to their debilitating effects on actively proliferating cells, an increasing body of evidence suggests that anticancer agents instead induce [...]

Mutations of p53, which inhibited the transformation of adenovirus early region 1A-expressing cells due to apoptosis, improved the survival of malignant cells that expressed oncogene activities during the early stages of tumor progression. Environment signals, which inhibited cell growth, stimulated apoptosis, which was involved in p53 stabilization.

Ionizing radiation and many chemotherapeutic agents induce apoptosis in cell possessing the E1A oncogene. It is also revealed that the p53 tumor suppressor is needed for the stimulation of the cell death process. Reaction of E1A-expressing fibroblasts with small doses of ionizing radiation or chemotherapeutic compounds induce apoptosis quickly. This reaction, however, has no effect on the viability of untransfected fibroblasts or E1A-expressing cells bereft of p53. At lower doses of ionizing radiation or chemotherapeutic compounds, the cytotoxic action of several anticancer agents is influenced by the genotype of the cell and not by the genotoxicity of the agent.

Murine embryonic stem cells were infected with the U3lacZ virus vector, resulting in the generation of lacZ gene fusions which could be detected by fluorescein di-beta-D-galactopyranoside and efficiently sorted using a fluorescence-activated cell sorter. The gene fusions could be passed into the germ line, indicating that the procedure does not affect the stem cell totipotency. Therefore, the procedure can be used to screen for genes involved in cell development and regulation.