Pairing morphology with gene expression in thyroid hormone-induced intestinal remodeling and identification of a core set of TH-induced genes across tadpole tissues.

Thyroid hormone (T3) plays a central role in vertebrate post-embryonic development, and amphibian metamorphosis provides a unique opportunity to examine T3-dependent developmental changes. To establish a molecular framework for understanding T3-induced morphological change, we identified a set of gene expression profiles controlled by T3 in the intestine via microarray analysis. Samples were obtained from premetamorphic Xenopus laevis tadpole intestines after 0, 1, 3, and 6 days of T3 treatment, which induces successive cell death and proliferation essential for intestinal remodeling. Using a set of 21,807 60-mer oligonucleotide probes representing >98% of the Unigene clusters, we found that 1997 genes were differentially regulated by 1.5-fold or more during this remodeling process and were clustered into four temporal expression profiles; transiently up- or downregulated and late up- or downregulated. Gene Ontology categories most significantly associated with these clusters were proteolysis, cell cycle, development and transcription, and electron transport and metabolism, respectively. These categories are common with those found for T3-regulated genes from brain, limb, and tail, although more than 70% of T3-regulated genes are tissue-specific, likely due to the fact that not all genes are annotated into GO categories and that GO categories common to different organs also contain genes regulated by T3 tissue specifically. Finally, a core set of upregulated genes, most previously unknown to be T3-regulated, were identified and enriched in genes involved in transcription and cell signaling.

Developmental arrest in Japanese medaka (Oryzias latipes) embryos exposed to sublethal concentrations of atrazine and arsenic trioxide.

Embryos of the Japanese medaka (Oryzias latipes) were exposed to serial concentrations of atrazine (0, 25, 50, and 100 ppm) and arsenic trioxide (0, 0.025, 0.05, 0.1 ppm) until hatching. Stasis of circulation, blood islands, titanic convulsions, tube heart and mortality were observed in atrazine-treated embryos. Each endpoint exhibited a concentration-response relationship. Only 4% of the embryos hatched in the 25 ppm, and none in the 50 and 100 ppm, probably due to cell death attributed to the embryos' inability to break from the chorion. With arsenic exposure, hatching was inversely correlated to chemical concentration: 86%, 75% and 54% for 0.025, 0.05 and 0.1 ppm, respectively. Hatching periods were also reduced from 7-13 days in controls to 7-11 days in arsenic-treated embryos. This observation was more pronounced with the 0.05 ppm concentration, showing a reduction of about 4 days. Despite this shortage in hatching time, there were no observable morphological abnormalities, as seen with atrazine. The ecological significance of these findings and implications for the development of sublethal toxicity tests using Japanese medaka embryos are important.

Cytotoxicity and transcriptional activation of stress genes in human liver carcinoma (HepG2) cells exposed to iprodione.

Iprodione (C13H13Cl2N3O3) is a broad spectrum dicarboximide fungicide used on a wide variety of crop diseases. It is used on vegetables, ornamentals, pome and stone fruit, root crops, cotton and sunflowers, to control a variety of fungal pests. Iprodione inhibits the germination of spores and the growth of the fungal mycelium. Experimental studies with mice have indicated that exposure to iprodione at dose levels 5 to 15 folds greater than the LOAEL for liver injury, induces microsomal enzyme activities, hepatocyte proliferation, hepatomegaly, centrilobular hypertrophy, diffuse hypertrophy, and an increase in lauric acid hydroxylation. Currently, there is no toxicological data available on human health effects associated with exposure to iprodione. In this research, we performed the MTT Assay for cell viability to assess the cytotoxicity of iprodione, and the CAT-Tox (L) assay to measure the induction of stress genes in thirteen recombinant cell lines generated from human liver carcinoma cells (HepG2). The cytotoxicity data indicated a strong concentration-response relationship with regard to iprodione toxicity. The percentages of cell viability were 100 +/- 0%, 128.0 +/- 41.4%, 97.5 +/- 37.7%, 70.1 +/- 35.4%, 33.5 +/- 16.1%, and 5.1 +/- 3.7% in 0, 31.3, 62.5, 125, 250, and 500 microg/mL, respectively. The LC50 was 208.3 +/- 83.3 microg/mL. Data obtained from the CAT-Tox (L) assay showed that iprodione is able to induce a significant number of stress genes in HepG2 cells. At 250 ug/mL exposure, the induction levels were 1.2 +/- 0.4, 50.1 +/- 17.8, 3.9 +/- 1.2, 16.8 +/- 7.2, 10.7 +/- 0.7, 1.8 +/- 0, 26.3 +/- 10.0, 7.2 +/- 2.4, 1.8 +/- 0.0, 6.8 +/- 1.3, 6.7 +/- 0.5, and 4.3 +/- 1.8 for CYP1A1, GSTYa, XRE, HMTIIA, c-fos, NF-kBRE, HSP70, CRE, RARE, GADD153, GADD45, and GRP78, respectively. These results indicate that the metabolism of iprodione involves Phase II biotransformation in the liver (XRE, GSTYa), and that this chemical has the potential to cause cell proliferation and/or inflammatory reactions (c-fos, NF-kB), proteotoxic effects (HSP70, GRP78), metabolic disruption (CRE), and DNA damage (GADD45, GADD153).