A microarray‐based comparative analysis of gene expression profiles in thyroid glands in amphibian metamorphosis: differences in effects between chemical exposure and food restriction

Abstract

Tadpoles during metamorphosis are sensitive to chemical exposure as shown in the amphibian metamorphosis assay, which is a method to detect effects of chemicals on the functions of hypothalamus‐pituitary‐thyroid axis. The present study reports existence of different modes of action between pyriproxyfen (PYR) and 6‐propyl‐2‐thiouracil (PTU) under different feeding conditions based on gene expression profiles (transcriptomics) in the thyroid glands of tadpoles of the African clawed frog, Xenopus laevis. PTU and PYR were exposed to the tadpoles during metamorphosis under normal (fed groups, both of PTU and PRY) and restricted feeding (fasted groups, PTU only) conditions; and effects were compared to control groups. Delayed development based on decreased Nieuwkoop and Faber developmental stage number without any histopathological changes was observed in the control of restricted feeding (control‐fasted) group, and the PYR group with reduced food consumption. Clear developmental retardation with typical thyroid histopathological changes was observed in the PTU groups. To find clusters of all samples based on their similarity of expression patterns, hierarchical clustering analysis using selected gene probes was conducted. It revealed gene profiles from samples of the PYR group were quite similar to those of the control‐fasted group, followed by the control group with normal feeding (control‐fed). The results suggest that key events in the thyroid glands of tadpoles induced by PYR should be quite similar to those of control‐fasted, and quite different from those of the PTU groups. Our findings demonstrated the usefulness of transcriptomics, which enabled recognition of the different modes of actions.

Inhibition of Metamorphosis, Thyroid Gland, and Skeletal Ossification Induced by Hexavalent Chromium in Bufo gargarizans Larvae

“…Histomorphological changes of the thyroid gland are used as a sensitive indicator for chemical‐induced thyrotoxicity (Grim et al 2009; Miyata and Ose 2012). Usually, histopathological changes were characterized by glandular atrophy, reduced colloid, and follicular cell hyperplasia (Zhao et al 2013; Ose et al 2019; Yang et al 2019). Several studies have shown that exposure to Cr (VI) affects thyroid gland histological characteristics in experimental organisms (Hassanin et al 2013; Mishra and Mohanty 2015).…”