Effects of Chronic Roundup Exposure on Medaka Larvae.

The use of glyphosate-based herbicides is increasing yearly to keep up with the growing demands of the agriculture world. Although glyphosate-based herbicides target the enzymatic pathway in plants, the effects on the endocrine systems of vertebrate organisms, mainly fish, are widely unknown. Many studies with glyphosate used high-exposure concentrations (mg/L), and the effect of environmentally relevant or lower concentrations has not been clearly understood. Therefore, the present study examined the effects of very low, environmentally relevant, and high concentrations of glyphosate exposure on embryo development and the thyroid system of Japanese medaka (Oryzias latipes). The Hd-rR medaka embryos were exposed to Roundup containing 0.05, 0.5, 5, 10, and 20 mg/L glyphosate (glyphosate acid equivalent) from the 8 h post-fertilization stage through the 14-day post-fertilization stage. Phenotypes observed include delayed hatching, increased developmental deformities, abnormal growth, and embryo mortality. The lowest concentration of glyphosate (0.05 mg/L) and the highest concentration (20 mg/L) induced similar phenotypes in embryos and fry. A significant decrease in mRNA levels for acetylcholinesterase (ache) and thyroid hormone receptor alpha (thrα) was found in the fry exposed to 0.05 mg/L and 20 mg/L glyphosate. The present results demonstrated that exposure to glyphosate formulation, at a concentration of 0.05 mg/L, can affect the early development of medaka larvae and the thyroid pathway, suggesting a link between thyroid functional changes and developmental alteration; they also showed that glyphosate can be toxic to fish at this concentration.

The PCOS-NAFLD Multidisease Phenotype Occurred in Medaka Fish Four Generations after the Removal of Bisphenol A Exposure.

As a heterogeneous reproductive disorder, polycystic ovary syndrome (PCOS) can be caused by genetic, diet, and environmental factors. Bisphenol A (BPA) can induce PCOS and nonalcoholic fatty liver disease (NAFLD) due to direct exposure; however, whether these phenotypes persist in future unexposed generations is not currently understood. In a previous study, we observed that transgenerational NAFLD persisted in female medaka for five generations (F4) after exposure to an environmentally relevant concentration (10 µg/L) of BPA. Here, we demonstrate PCOS in the same F4 generation female medaka that developed NAFLD. The ovaries contained immature follicles, restricted follicular progression, and degenerated follicles, which are characteristics of PCOS. Untargeted metabolomic analysis revealed 17 biomarkers in the ovary of BPA lineage fish, whereas transcriptomic analysis revealed 292 genes abnormally expressed, which were similar to human patients with PCOS. Metabolomic-transcriptomic joint pathway analysis revealed activation of the cancerous pathway, arginine-proline metabolism, insulin signaling, AMPK, and HOTAIR regulatory pathways, as well as upstream regulators esr1 and tgf signaling in the ovary. The present results suggest that ancestral BPA exposure can lead to PCOS phenotypes in the subsequent unexposed generations and warrant further investigations into potential health risks in future generations caused by initial exposure to EDCs.

Potassium perchlorate effects on primordial germ cells of developing medaka larvae.

Perchlorate is a chemical compound commonly used in military artillery and equipment. It has been detected in drinking water, air, soil, and breast milk. Exposure of humans to perchlorate can occur in the theater of war and areas adjacent to military training grounds. A high concentration of perchlorate has been found to affect reproduction in vertebrates, including fish. However, whether environmental concentrations of perchlorate can affect primordial germ cells (PGCs), the founders of sperm and eggs, is not clearly understood. In the present study, we examined the effects of 0, 10, 100, and 1000 µg/L potassium perchlorate exposure on the embryonic development of medaka and their PGCs. Perchlorate exposure delayed hatching time, reduced heartbeat, inhibited migration of PGCs, and increased developmental deformities in the larvae. The 10 and 20 mg/L concentrations of perchlorate were lethal to embryos, whereas vitamin C co-treatment (1 mg/L) completely blocked perchlorate-induced mortality. RNA-seq analysis of isolated PGCs showed a non-linear pattern in expression profiles of differentially altered genes. Significantly upregulated genes were found in PGCs from the 10 and 1000 µg/L groups, whereas the 100 µg/L groups showed the highest number of significantly downregulated genes. Gene ontology analysis predicted differentially expressed genes to be involved in proteolysis, metabolic processes, peptides activity, hydrolase activity, and hormone activity. Among the cellular components, extracellular, intracellular, sarcoplasmic, and 6-phosphofructokinase and membrane-bounded processes were affected. Ingenuity Pathway Analysis of PGC transcriptomes revealed thyroid hormone signaling to be affected by all concentrations of perchlorate. The present results suggested that perchlorate affected the development of medaka larvae and vitamin C was able to ameliorate perchlorate-induced embryo mortality. Additionally, perchlorate altered the global transcriptional network in PGCs in a non-linear fashion suggesting its potential effects on developing germ cells and fertility.