Adverse effects from low dietary and environmental boron exposure on reproduction, development, and maturation in Xenopus laevis

In two separate 120-d depletion studies conducted previously, adult frogs (Xenopus laevis) fed a low boron diet (-B; 62 mu g B/kg feed) for either 28 d or 12 d produced a greater proportion of necrotic eggs and fertilized embryos that abnormally gastrulated at a greater rate and were substantially less viable at 96 h of development when compared to embryos from adults administered a diet supplemented with boron (+B; 1850 mu g B/kg feed). These studies showed that 28 d or 120 d of low boron markedly impaired normal reproductive function in adult X. laevis and that no embryos from -B administered adults survived and developed normally, suggesting that boron is nutritionally essential for reproduction and development in Xenopus. These studies also demonstrated that both the incidence and severity of adverse effects were greatly increased after 120 d on the -B diet, in comparison to observations after just 28 d on the -B diet. Complete concentration-response curves were developed for boron in Xenopus using a 4 d embryo-larval developmental model (Frog Embryo Teratogenesis Assay: Xenopus [FETAX]), again documenting nutritionally essential, as well as toxic, concentration ranges. Deleterious developmental effects were induced in this assay at culture media concentrations of <0.3 mu M B and >4980 mu M B. Four-d Xenopus embryo-larval development within the range of 0.5-3320 mu M B was shown to be normal. An evaluation of the impact of -B administration on Xenopus maturation indicated that when compared to their +B counterparts, -B maintained larvae showed markedly slower rates of metamorphosis, specifically tail resorption. Results of these studies further support and define the nutritional essentiality of boron in Xenopus reproduction and development. J. Trace Elem. Exp. Med. 12:175-185, 1999. (C) 1999 Wiley-Liss, Inc.