IGF-2 and Growth of the Conceptus
IGF-2 production by the conceptus begins to alter its size from E10.5. Substantial quantities of Igf2 mRNA can first be detected by autoradiography at E5.5 in trophectoderm derivatives, at E6.5-7.0 in the extra-embryonic endoderm and extra-embryonic mesoderm, and at E7.5 in the mesoderm of the embryo. Immunohistochemistry suggests that at least some of this Igf2 mRNA is translated into protein by E8. The absence of Igf2 transcripts markedly reduces the wet weight of the fetus at about E11 and the wet weight of the placenta at about E13. The reduced size of mice lacking an active paternal Igf2 gene persists throughout life, despite the expression of the maternal allele in the exchange tissues around the central nervous system. flovent inhaler
Subtle effects of IGF-2 levels on cell interactions might precede the large effects on wet weight. For instance, exogenous IGF-2 promotes trophoblast giant cell transformation in cell culture. In the late blastocyst, the ICM orients and induces the proliferation of the trophectoderm, and it has been argued that the mechanical properties of the growing extraembryonic ectoderm derivative of the trophectoderm shape the growing ICM descendants.