Insulin-related peptides and the two-cell block to development in pre-implantation mouse embryos

In many mammalian embryos development in vitro is arrested after the first zygotic division, a phenomenon known as the two-cell block. In the mouse several strains exhibit a two-cell block to further development and it was the purpose of this investigation to determine whether the inability of embryos to progress through the block was due to lack of insulin or insulin-like growth factors (IGFs) in the medium. Several factors have been implicated in the two-cell block, amongst which oxidative stress, glucose and missing maternal factors have been examined to date. Because of their anabolic and anti-apoptotic properties, IGFs are good candidates for such missing maternal factors. Using MF1 strain mice and M16 medium we have examined the effects of IGF-I, II and insulin on the two-cell block. No effects were discernable at concentrations known to support development of non-blocking embryos and we conclude that the IGFs and insulin may be excluded as critical factors in the two-cell block under the culture conditions used.