M. Pantaleon et al., FUNCTIONAL GROWTH-HORMONE (GH) RECEPTORS AND GH ARE EXPRESSED BY PREIMPLANTATION MOUSE EMBRYOS - A ROLE FOR GN IN EARLY EMBRYOGENESIS, Proceedings of the National Academy of Sciences of the United Statesof America, 94(10), 1997, pp. 5125-5130
The results of this study challenge the widely held view that growth h
ormone (GH) acts only during the postnatal period. RNA phenotyping sho
ws transcripts for the GH receptor and GH-binding protein in mouse pre
implantation embryos of all stages from fertilized eggs (day 1) to bla
stocysts (day 4). An antibody specific to the cytoplasmic region of th
e GH receptor revealed receptor protein expression, first in two-cell
embryos, the stage of activation of the embryonic genome (day 2), and
in all subsequent stages, In cleavage-stage embryos this immunoreactiv
ity was localized mainly to the nucleus, but clear evidence of membran
e labeling was apparent in blastocysts. GH receptor immunoreactivity w
as also observed in cumulus cells associated with unfertilized oocytes
but not in the unfertilized oocytes. The blastocyst receptor was demo
nstrated to be functional, exhibiting the classic bell-shaped dose-res
ponse curves for GH stimulation of both 3-O-methyl glucose transport a
nd protein synthesis. Maximal stimulation of 40-50% was seen for both
responses at less than 1 ng/ml recombinant GH, suggesting a role for m
aternal GK. However mRNA transcripts for GH were also detected from th
e morula stage (day 3) by using reverse transcription-PCR, and GH immu
noreactivity was seen in blastocysts. These observations raise the pos
sibility of a paracrine/autocrine GH loop regulating embryonic develop
ment in its earliest stages.