Adverse effects of a low boron environment on the preimplantation development of mouse embryos in vitro

We have used a preimplantation embryo culture system to investigate the effects of boron (B) deficiency on early mouse development. To test the influence of low boron concentration in the medium, two-cell embryos collected from CD-1 mice fed a commercial stock high boron diet were cultured for 72 h in control boron (B+), or boron-free (B-) media. Preimplantation development was similar in the two groups over the 72-h period (Study 1). To investigate the influence of maternal boron status on early embryonic development, mice were fed a low boron (0.04 μg B/g, LOW), or a suppplemented boron (2.05 μg B/g, SUPP) purified diet, or a high boran (11.8 μg B/g, STOCK) commercial stock diet. In Study 2A, two-cell embryos were collected after the females had been fed the diets for 10, 12, or 16 weeks. Embryos were cultured in B+ medium. In Study 2B, two-cell embryos were cultured after the females had been fed the diets for 16 weeks, and the embryos were cultured in B-medium. In both studies, liver and tibia boron concentrations were lower in LOW fed mice than in mice fed the SUPP or STOCK diets. The in vitro development of two-cell embryos collected from mice fed either one of the boron purified diets was not severely impaired when they were cultured in B+ medium. However, two-cell embryos from the LOW diet had a lower frequency of blastocyst formation (83.5%, LOW vs. 90.1%, SUPP), and an increased frequency of degenerate embryos (13.0%, LOW vs. 8.0%, SUPP) after 72 h of culture compared to embryos from the SUPP diet. Exposure to dietary and medium boron deficiency significantly compromised the in vitro development of two-cell embryos compared to dietary boron deficiency alone. Low dietary boron combined with low boron in the medium resulted in the highest percentage of degenerate embryos (57.0%). Collectively, these data support the concept that boron deficiency impairs early embryonic development in rodents.