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Insulin-like growth factor-1 stimulates growth of mouse preimplantation embryos in vitro
1Department of Physiology and Pharmacology, University of Queensland, Brisbane, Australia.
Because recent studies have particularly implicated the insulin growth factor family in early development, the effects of insulin-like growth factor (IGF-1) on the development of mouse embryos in vitro were investigated in detail. When added to the medium for culture of two-cell embryos, IGF-1 stimulated the number of cells in the resultant blastocysts after 54 hr, entirely by increasing the number of cells in the inner cell mass (ICM) (16.0 +/- 0.5 vs. 12.6 +/- 0.5 cells/ICM). This stimulation was also achieved when ICMs were isolated from blastocysts prior to culture for 24 hr with IGF-1 (22.3 +/- 1.0 vs. 17.5 +/- 0.8 cells/ICM). There was no effect on IGF-1 on trophectoderm (TE) cell proliferation. In morphology studies, IGF-1 also increased the proportion of blastocysts (62% +/- 3% vs. 49% +/- 4%) while decreasing the number of embryos remaining as morulae (32% +/- 3% vs. 38% +/- 2%) or in the early cleavage stages (7% +/- 3% vs. 13% +/- 3%) after 54 hr culture from the two-cell stage. All these effects were achieved with EC50s of approximately 60 pM IGF-1, which is in the range for IGF-1 receptor mediation; however, cross reaction with insulin, IGF-2, or other unknown receptors is not excluded. Nonetheless, the results show that physiological concentrations of IGF-1 (17-170 pM, 0.1-1 ng/ml), which have been observed in the reproductive tract, affect the early embryo, suggesting a normal role for this factor in the regulation of growth of the developing conceptus before implantation.
Because recent studies have particularly implicated the insulin growth factor family in early development, the effects of insulin-like growth factor (IGF-1) on the development of mouse embryos in vitro were investigated in detail. When added to the medium for culture of two-cell embryos, IGF-1 stimulated the number of cells in the resultant blastocysts after 54 hr, entirely by increasing the number of cells in the inner cell mass (ICM) (16.0 +/- 0.5 vs. 12.6 +/- 0.5 cells/ICM). This stimulation was also achieved when ICMs were isolated from blastocysts prior to culture for 24 hr with IGF-1 (22.3 +/- 1.0 vs. 17.5 +/- 0.8 cells/ICM). There was no effect on IGF-1 on trophectoderm (TE) cell proliferation. In morphology studies, IGF-1 also increased the proportion of blastocysts (62% +/- 3% vs. 49% +/- 4%) while decreasing the number of embryos remaining as morulae (32% +/- 3% vs. 38% +/- 2%) or in the early cleavage stages (7% +/- 3% vs. 13% +/- 3%) after 54 hr culture from the two-cell stage. All these effects were achieved with EC50s of approximately 60 pM IGF-1, which is in the range for IGF-1 receptor mediation; however, cross reaction with insulin, IGF-2, or other unknown receptors is not excluded. Nonetheless, the results show that physiological concentrations of IGF-1 (17-170 pM, 0.1-1 ng/ml), which have been observed in the reproductive tract, affect the early embryo, suggesting a normal role for this factor in the regulation of growth of the developing conceptus before implantation.