Inbred wild type mouse strains have distinct spontaneous morphological phenotypes

The mouse is the most commonly used animal for modelling human disease. New approaches for generating genetically manipulated mouse models to represent human disease, as well as target the function of specific genes, has increased the importance of mice in biomedical science. For the correct interpretation of alterations in mouse phenotype the basic morphology of background mouse strains must be known. Despite on-going efforts to create publicly available baseline phenotypic data, the information concerning spontaneous lesions in wild-type mice is incomplete and scattered so far, and further studies are needed. We addressed this problem by screening haematoxylin-eosin stained sections of brain, reproductive organs, urinary bladder, kidney, thyroid, parathyroid, heart, lung, spleen, thymus, lymph nodes, adrenal glands, stomach, intestine, liver, skin and pancreas of six commonly used inbred mouse strains (C57BL6/J, C57BL6/NTac, C3HeB/FeJ, BALB/cByJ, 129P2/OlaHsd and FVB/N) for inherent spontaneous morphological lesions. Interesting spontaneous phenotypes were seen in morphology of the liver, pancreas, adrenal glands, lungs, intestines and heart. In conclusion, care should be taken when choosing the background mouse strain for genetic manipulations, since different mouse strains harbour different inherent lesions that can affect the function of targeted genes, interpretation of results and translation of results to model human disease.

Responses of PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) in MCF-7 cells are culture condition dependent

To compare the effects of the food toxin 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) and estradiol in hormone-responsive MCF-7 cells, the cells were exposed to different concentrations of either PhIP or estradiol. The effect of various culture conditions (e.g. phenol red, FBS, vehicle (DMSO/EtOH) and seeding density) on responses was studied. Cells were continuously grown with steroid-containing or -deprived medium, or switched from steroid-containing to -deprived medium for the experiments to minimize the effect of background estrogenicity. Effects of PhIP and estradiol on cell viability and proliferation were determined by ATP analysis and Ki-67 immunocytochemistry. Expression of estrogen receptor alpha, cell stress markers (p53 and ERK) and estrogen responsive proteins (c-myc and ERK) were immunoblotted. All concentrations of estradiol induced cell proliferation, viability and changes in protein expression, typical for estrogenic responses. PhIP, however, increased viability only at low concentrations and depending on culture conditions. No changes in protein expressions by PhIP were noted, not even when switching cells from steroid-containing to -deprived medium which down-regulated the expression of proteins at basal level. Vehicle affected significantly viability, especially after exposure to PhIP, but not protein expression while medium changes affected both. In conclusion, the effects of PhIP and estradiol in MCF-7 cells are dependent on culture conditions. The detected PhIP-induced changes are weaker compared to those induced by estradiol.

Thapsigargin has similar effect on p53 protein response to benzo[a]pyrene-DNA adducts as TPA in mouse skin

The level of p53 tumor suppressor protein increases in response to DNA damage caused by benzo[a]pyrene (B[a]P). The most used tumor promoter in the two step mouse skin carcinogenesis model, 12-O-tetradecanoylphorbol-13-acetate (TPA) decreases this response in mouse skin. In this study the effect of another promoter, thapsigargin was tested on B[a]P-induced p53 response using immunohistochemistry, western blotting and immunoelectron microscopy. We also studied the localization of p53 protein after treatments with BP and TPA or thapsigargin. Thapsigargin had a TPA-like effect on the acute induction of p53 protein related to benzo[a]pyrene-7, 8-diol-9,10-epoxide-DNA adducts in the skin of C57BL/6 mouse. After B[a]P treatment, there was slightly more putatively wild-type p53 protein in nuclei than in cytoplasm of the cells. Neither TPA nor thapsigargin affected the localization of p53 protein. Since both compounds increase the level of intracellular calcium, the inhibition of the p53 response may depend on the level of intracellular calcium. Inhibition of the putatively genome-protecting increase in p53 protein may be one of the critical effects of tumor promoters.