Expression Levels of EGF, TGF-α, and EGF-R Are Significantly Reduced in Pre-Implantation Cloned Mouse Embryos

Abstract

Altered expression of genes encoding mitogenic growth factors thought to play key regulatory roles in preimplantation development may contribute to poor cloning efficiency. In this study, we compared the pattern, timing, and level of expression of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-␣) genes and their cognate receptor EGF-R in mouse embryos derived by cloning with in vivo-(naturally fertilized) and in vitro-fertilized embryos at four preimplantation stages of development. In cloned embryos, EGF, TGF-␣, and EGF-R expression levels were nearly undetectable, while expression of a housekeeping gene, transcription factor SP1, was normal. In contrast, growth factor genes were expressed in in vitro-fertilized embryos, although significantly less than in in vivo embryos (p Ͻ 0.05). In all embryos examined, the timing and pattern of gene expression were similar. Expression in the gravid uterus paralleled that in preimplantation embryos, while no expression was measured in non-gravid uteri. Our results lead us to speculate that altered levels of expression of EGF, TGF-␣, and EGF-R impair mammalian development, which could account for the poor survival potential of cloned mouse embryos. 267