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 emb ryos that abnormally gastrulated at a greater rate and were substantially l ess viable at 96 h of development when compared to embryos from adults admi nistered a diet supplemented with boron (+B; 1850 mu g B/kg feed). These st udies showed that 28 d or 120 d of low boron markedly impaired normal repro ductive function in adult X. laevis and that no embryos from -B administere d adults survived and developed normally, suggesting that boron is nutritio nally essential for reproduction and development in Xenopus. These studies also demonstrated that both the incidence and severity of adverse effects w ere greatly increased after 120 d on the -B diet, in comparison to observat ions after just 28 d on the -B diet. Complete concentration-response curves were developed for boron in Xenopus using a 4 d embryo-larval developmenta l model (Frog Embryo Teratogenesis Assay: Xenopus [FETAX]), again documenti ng nutritionally essential, as well as toxic, concentration ranges. Deleter ious developmental effects were induced in this assay at culture media conc entrations of <0.3 mu M B and >4980 mu M B. Four-d Xenopus embryo-larval de velopment within the range of 0.5-3320 mu M B was shown to be normal. An ev aluation of the impact of -B administration on Xenopus maturation indicated that when compared to their +B counterparts, -B maintained larvae showed m arkedly slower rates of metamorphosis, specifically tail resorption. Result s 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.