Immunocompetence and alterations in hepatic gene expression in rainbow trout exposed to CdS/CdTe quantum dots.

Cadmium (Cd) tellurium quantum dots (QDs) are long-lived fluorescent nanocrystals that have the ability to produce potentially toxic reactive oxygen species at the surface of the nanoparticle and release toxic cadmium ions. The purpose of this study was to examine the sublethal effects of CdS/CdTe QDs and dissolved Cd on the immune system of rainbow trout. Changes in hepatic gene expression were also monitored to provide insight on the mode of action of both forms of cadmium. Oncorhynchus mykiss fish were exposed to increasing concentrations of CdS/CdTe or dissolved Cd (CdSO(4)) for 48 h at 15 degrees C. The anterior head kidney was analyzed for leukocyte count, viability and phagocytic activity. The livers were harvested and prepared for gene expression analysis using a DNA microarray comprised of 207 stress-related genes. An analysis of total Cd in the aquarium water revealed that the nominal concentrations corresponded well to the actual concentrations and that a small proportion (0.4%) of Cd in the QDs was found in the dissolved fraction. Exposure to QDs led to significant reductions in leukocyte counts, viability and both resting and active phagocytic activity. On a mass concentration basis, QDs were more potent than dissolved Cd in suppressing immunocompetence in rainbow trout. The analysis revealed that both forms of Cd were strong inducers of metallothionein and CP2K1 gene expressions, which are respectively involved in metal detoxification processes and xenobiotic transformation/inflammation conditions. The analysis revealed different modes of action for each form of Cd. For QDs, 25 genes specific to QDs and related to the immune endpoints were found. The genes were involved in inflammation, xenobiotic biotransformation and endocrine system (including the induction of vitellogenin and its receptor). The effect for dissolved Cd was narrower than for QDs, with 9 genes specific to dissolved Cd being strongly correlated with the observed effects on immunocompetence. The involved genes were binding and transport of various solutes (urea, sodium, potassium) and the complement system. The present study revealed that each form of Cd produced a different pattern of gene expression and lowered fish immunocompetence.

Genistein prevents thyroid hormone-dependent tail regression of Rana catesbeiana tadpoles by targetting protein kinase C and thyroid hormone receptor alpha.

Thyroid hormone (TH)-regulated gene expression is mainly mediated by TH binding to nuclear thyroid hormone receptors (TRs). Despite extensive studies in mammalian cell lines that show that phosphorylation signaling pathways are important in TH action, little is known about their roles on TH signaling in vivo during development. Anuran metamorphosis is a postembryonic process that is absolutely dependent upon TH and tadpole tail resorption can be precociously induced by exogenous administration of 3,5,3'-triiodothyronine (T(3)). We demonstrate that genistein (a major isoflavone in soy products and tyrosine kinase inhibitor) and the PKC inhibitor (H7) prevent T(3)-induced regression of the Rana catesbeiana tadpole tail. T(3)-induced protein kinase C tyrosine phosphorylation and kinase activity are inhibited by genistein while T(3)-induced up-regulation of TRbeta mRNA, but not TRalpha mRNA, is significantly attenuated, most likely through inhibition of T(3)-dependent phosphorylation of the TRalpha protein. This phosphorylation may be modulated through PKC. These data demonstrate that T(3) signaling in the context of normal cells in vivo includes phosphorylation as an important factor in establishing T(3)-dependent tail regression during development.

Expression of novel ING variants is regulated by thyroid hormone in the Xenopus laevis tadpole.

The candidate tumor suppressor gene, ING1, encodes several protein isoforms as a result of alternative splicing that may possess agonistic and antagonistic roles in the control of cell proliferation and apoptosis. Recently a related gene, ING2, was isolated in human whose expression is increased in adenocarcinomas. Little is known about the cellular function and regulation of these ING family members, but the fact that ING proteins contain a plant homeodomain finger suggests that these proteins may modulate transcription factor-mediated pathways. To elucidate how ING may interact in different tissues to modulate function, we used amphibian metamorphosis as a model system in which a single stimulus, thyroid hormone (TH), initiates tissue-specific proliferation, differentiation, and apoptosis. We have isolated the first Xenopus laevis ING2 and demonstrate that transcript levels increase in response to TH treatment. We provide evidence for the existence of splice variants that are differentially expressed in tissues with different TH-induced fates. Western blots using an antibody directed against the highly conserved C-terminal end of ING proteins reveal a tissue-specific pattern of ING isoform expression in adult Xenopus tissues. Analyses of premetamorphic tadpole tissues show a TH-induced accumulation of ING proteins in tail, whereas the levels in the leg are not affected. This TH-induced accumulation is also observed in serum-free tail organ cultures and is prevented by inhibitors of tail apoptosis. Therefore, this work presents the first link between ING expression and a hormonally regulated nuclear transcription factor-mediated apoptotic response opening the possibility that ING family members may be involved in transducing the signal initiated by TH that determines cell fate.