Cardiovascular gene expression profiles of dioxin exposure in zebrafish embryos

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Society of Toxicology for personal use, not for redistribution. The definitive version was published in Toxicological Sciences 85 (2005): 683-693, doi:10.1093/toxsci/kfi116.2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a widespread environmental contaminant that causes altered heart morphology, circulatory impairment, edema, hemorrhage, and early life stage mortality in fish. TCDD toxicity is largely dependent upon the aryl hydrocarbon receptor, but understanding of the molecular mechanism of cardiovascular embryotoxicity remains incomplete. In order to identify genes potentially involved in cardiovascular impacts, we constructed custom cDNA microarrays consisting of 4,896 zebrafish adult heart cDNA clones and over 200 genes with known developmental, toxicological, and housekeeping roles. Gene expression profiles were obtained for 3-day old zebrafish following early embryonic exposure to either 0.5 or 5.0 nM TCDD. 516 clones were significantly differentially expressed (p-value < 0.005) under at least one treatment condition; 123 high-priority clones were selected for further investigation. CYP1A, CYP1B1, and other members of the AHR gene battery, were strongly and dose-dependently induced by TCDD. Importantly, altered expression of cardiac sarcomere components, including cardiac troponin T2 and multiple myosin isoforms, was consistent with the hypothesis that TCDD causes dilated cardiomyopathy. Observed increases in expression levels of mitochondrial energy transfer genes also may be related to cardiomyopathy. Other TCDD-responsive genes included fatty acid and steroid metabolism enzymes, ribosomal and signal transduction proteins, and 18 ESTs with no known protein homologs. As the first broadscale study of TCDD-modulated gene expression in a non-mammalian system, this work provides an important perspective on mechanisms of TCDD toxicity.This work was supported by funding from the National Institutes of Health

Identification of novel ciliogenesis factors using a new in vivo model for mucociliary epithelial development

Mucociliary epithelia are essential for homeostasis of many organs and consist of mucus-secreting goblet cells and ciliated cells. Here, we present the ciliated epidermis of Xenopus embryos as a facile model system for in vivo molecular studies of mucociliary epithelial development. Using an in situ hybridization-based approach, we identified numerous genes expressed differentially in mucus-secreting cells or in ciliated cells. Focusing on genes expressed in ciliated cells, we have identified new candidate ciliogenesis factors, including several not present in the current ciliome. We find that TTC25-GFP is localized to the base of cilia and to ciliary axonemes, and disruption of TTC25 function disrupts ciliogenesis. Mig12-GFP localizes very strongly to the base of cilia and confocal imaging of this construct allows for simple visualization of the planar polarity of basal bodies that underlies polarized ciliary beating. Knockdown of Mig12 disrupts ciliogenesis. Finally, we show that ciliogenesis factors identified in the Xenopus epidermis are required in the midline to facilitate neural tube closure. These results provide further evidence of a requirement for cilia in neural tube morphogenesis and suggest that genes identified in the Xenopus epidermis play broad roles in ciliogenesis. The suites of genes identified here will provide a foundation for future studies, and may also contribute to our understanding of pathological changes in mucociliary epithelia that accompany diseases such as asthma.close49

Inferring crustal structure in the Aleutian island arc from a sparse wide-angle seismic data set

Compressional seismic travel times from a relatively sparse wide-angle data set hold key information on the structure of a 800 km long section of the central Aleutian arc. Since the source and receiver locations form a swath along the arc crest that is similar to50 km wide, we trace rays in 3-D for a collection of 8336 seismic refraction and reflection arrivals. We investigate variations in seismic velocity structure parallel to the Aleutian arc, assuming that our result represents average crustal structure across the arc. We explore seismic velocity models that consist of three crustal layers that exhibit smooth variations in structure in the 2-D vertical plane. We consider the influence of additional constraints and model parameterization in our search for a plausible model for Aleutian arc crust. A tomographic inversion with static corrections for island stations reduces the data variance of a 1-D starting model by 91%. Our best model has seismic velocities of 6.0-6.5 km/s in the upper crust, 6.5-7.3 km/s in the middle crust, and 7.3-7.7 km/s in the lower crust and a total crustal thickness of 35-37+/-1 km. A resolution analysis shows that features having a horizontal scale less than 20 km cannot be imaged, but at horizontal length scales of similar to50 km most model features are well resolved. The study indicates that the Aleutian island arc crust is thick compared to other island arcs and strongly stratified and that only the upper 60% of the arc crust has seismic velocities that are comparable to average seismic velocities in continental crust