Expression and function of amphiregulin during murine preimplantation development

Amphiregulin (Ar) is an EGF receptor ligand that functions to modulate the growth of both normal and malignant epithelial cells. We asked whether mouse preimplantation embryos express Ar, and if so, what the function of Ar is during preimplantation development. We used RT‐PCR to show expression of Ar mRNA in mouse blastocysts, and using a polyclonal anti‐Ar antibody and indirect immunofluorescence, we detected the presence of Ar protein in morula‐ and blastocyst‐stage embryos. Ar protein was present in both the cytoplasm and nucleus in both morulae‐ and blastocyst‐stage embryos, which is similar to Ar distribution in other cell types. Embryos cultured in Ar developed into blastocysts more quickly and also exhibited increased cell numbers compared to control embryos. In addition, 4‐cell stage embryos cultured in an antisense Ar phosphorothioate‐modified oligodeoxynucleotide (S‐oligo) for 48 hr exhibited slower rates of blastocyst formation and reduced embryo cell numbers compared to embryos exposed to a random control S‐oligo. TGF‐α significantly improved blastocyst formation, but not cell numbers, for embryos cultured in the antisense Ar S‐oligo. From these observations, we propose that Ar may function as an autocrine growth factor for mouse preimplantation embryos by promoting blastocyst formation and embryo cell number. We also propose that blastocyst formation is stimulated by Ar and TGF‐α, while Ar appears to exert a greater stimulatory effect on cell proliferation than does TGF‐α in these embryos. Mol. Reprod. Dev. 47:271–283, 1997. © 1997 Wiley‐Liss, Inc.