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During digestive organogenesis, the primitive gut tube (PGT) undergoes dramatic elongation and forms a lumen lined by a single-layer of epithelium. In Xenopus, endoderm cells in the core of the PGT rearrange during gut elongation, but the morphogenetic mechanisms controlling their reorganization are undetermined. Here, we define the dynamic changes in endoderm cell shape, polarity, and tissue architecture that underlie Xenopus gut morphogenesis. Gut endoderm cells intercalate radially, between their anterior and posterior neighbors, transforming the nearly solid endoderm core into a single layer of epithelium while concomitantly eliciting “radially convergent” extension within the gut walls. Inhibition of Rho/ROCK/Myosin II activity prevents endoderm rearrangements and consequently perturbs both gut elongation and digestive epithelial morphogenesis. Our results suggest that the cellular and molecular events driving tissue elongation in the PGT are mechanistically analogous to those that function during gastrulation, but occur within a novel cylindrical geometry to generate an epithelial-lined tube. Developmental Dynamics 238:3111–3125, 2009. © 2009 Wiley-Liss, Inc.

Early life stages of fishes have been shown to be especially susceptible to the toxic effects of heavy metal pollution. In this study, fathead minnow (Pimephales promelas) embryos were exposed in the laboratory to a graded series of aqueous methyl mercury concentrations under continuous-flow conditions. A number of toxicological endpoints were examined including; acute toxicity, bioaccumulation, protein production, impact on mitosis, gross and histopathology. Acute toxicity, reported as LC50 values of methyl mercury, ranged from 221 microg/l (95% C.I. 246-196 microg/l) for 24-h tests to 39 microg/l (95% C.I. 54-24 microg/l) for 96-h exposures. Fathead minnow embryos were shown to rapidly take up mercury from the surrounding water. Mercury levels in embryos reached levels of 2.80 microg/g wet weight after 96 h exposure to 40 microg/l methyl mercury. An initial elevation of total protein in embryo was observed in embryos exposed to 25 microg/l methyl mercury during the first 12 h of development. At later stages, significantly lower levels of protein/microg embryo were observed. Methyl mercury had no effect on mitotic stages (p=0.05) in early, cleaving blastula-stage embryos. Live embryos and serial sections were utilized to characterize changes in embryo morphology and histopathology.

Environmental levels of heavy metals like mercury have increased significantly over the last 100 years in response to anthropogenic activities. More recently the increase in acid precipitation may make the situation worse in that it appears to increase the production of methyl mercury (MeHg) in the surface waters and benthic regions. Concentrations of mercury in surface waters are normally relatively low in the ng/L range, yet levels of mercury in fish tissue in the mg/L range are not uncommon. There have been several well-publicized accounts of acute mercury poisoning from consuming highly contaminated fish. Less is known about the health risks associated with consumption of fish with low levels of mercury contamination. Human embryos are especially sensitive to MeHg's teratogenic effects. For example, psychomotor retardation is a common outcome of fetal MeHg exposure. Such neural effects may be the result of abnormal migration of neurons during development. A number of different species have been utilized to investigate the effects of mercury on teleost development. Coho salmon, like all teleostean embryos possess mitotic cells that provide a useful model for the study of MeHg teratogenesis. Due to their large size, coho salmon embryos are easily observed and maintained in the laboratory.more » In addition large numbers of eggs are available from one female thus minimizing effects of variability among individuals. The objective of the present study is to characterize the toxic levels of MeHg and study their uptake. In addition some of the teratogenic effects of MeHg on coho salmon embryos will be described. 16 refs., 3 figs., 1 tab.« less

The environmental levels of aromatic hydrocarbons present in freshwater systems have been poorly characterized. This study examines the effect of toluene, a major water-soluble component of petroleum fuels on teleost development under controlled conditions. The fathead minnowPimephales promelas Rafinesque, was chosen as a model teleost for this study. Live embryos as well as serial sections of paraffin-embedded embryos were examined to determine effects of the toxicant. The toluene concentrations utilized ranged from 30 to 45 mg/L. Abnormalities noted under these conditions included distorted embryonic axis, abnormal heart and circulatory system development, hydration and swelling of the pericardial coelom, hemorrhaging, an overall stunted appearance, microphthalmia, and a unique migration of the ventrally located yolk syncytial layer and its associated nuclei.

Toxic organic mercury compounds, especially methyl mercury (MeHg), have been responsible for severe environmental contamination. Industrial effluents of inorganic or metallic mercury are methylated by aquatic organisms leading to transfer and bioconcentration of MeHg up the food chain to fish and man. In vivo mammalian and teleostean (bony fish) models have provided useful data on mercury toxicity; cultures of animal cells have been used to investigate the toxic actions of heavy metals such as mercury. The present study was designed to determine if RTG-2 cells, a fibroblast-like line derived from rainbow trout (Salmo gairdneri) gonads, would provide a highly controlled system in which to study the mercury-cell interaction. A mammalian cell line derived from Chinese hamster ovary (CHO)2 and known to be sensitive to MeHg3 was chosen as a positive control. The specific objective was to determine the effect of MeHg on RTG-2 and CHO cell viability and ultrastructure.