The reverse transcription-polymerase chain reaction (RT-PCR) was used
to determine the patterns of expression for several growth factor liga
nd and receptor genes during ovine preimplantation development. Transc
ripts for insulin-like growth factor (IGF)-I, IGF-II, and the receptor
s for insulin and IGF-I were detected throughout ovine preimplantation
development from the 1-cell to the blastocyst stage. Transforming gro
wth factor alpha (TGFalpha) transcripts were also detected throughout
ovine preimplantation development. The mRNAs encoding basic fibroblast
growth factor (bFGF) were detected in all stages of the ovine preimpl
antation embryo, although the relative abundance of this transcript co
nsistently decreased from the 1-cell to the blastocyst stage, suggesti
ng that it may represent a maternal transcript in early sheep embryos.
Transcripts encoding ovine trophoblast protein (oTP) were detected on
ly within blastocyst-stage embryos. Primary ovine oviduct cell culture
s express the transcripts for IGF-II, IGF-I, TGFalpha, bFGF, TGFbeta1,
and the receptors for insulin and IGF-I, suggesting that paracrine gr
owth factor circuits may exist between the oviduct epithelium and the
early ovine embryo. Transcripts for insulin, epidermal growth factor (
EGF), and nerve growth factor (NGF) were not detected in any stage of
the ovine preimplantation embryo or within the oviduct cell preparatio
ns. The expression of growth factor transcripts very early in mammalia
n development would predict that these molecules fulfil a necessary ro
le(s) in supporting the progression of early embryos through the preim
plantation interval. Our future efforts will be directed to understand
ing the nature of these putative regulatory pathways.