Insulin‐like growth factor‐1 stimulates growth of mouse preimplantation embryos in vitro

Abstract

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.

Effects of oxygen tension and IGF-I on HIF-1α protein expression in mouse blastocysts

“…Indeed, Herrler et al [16] suggested that IGF-I in preimplantation rabbit embryos was capable of reducing apoptosis and increasing cell proliferation. Also, several studies reported that IGF-I promotes pre-implantation embryo development and cell numbers in many species, including mouse [15], cow [18], and human [17]. The antiapoptotic effects of IGF-I generally act through a phosphatidylinositol 3-kinase (PI3K)/Akt signal pathway which subsequently inactivates pro-apoptotic proteins such as Bad and caspase-9 and stimulates anti-apoptotic proteins, including Bcl-2, a number of transcription factors and translational regulatory proteins [41,42].…”

“…This occurs independently of oxygen tension, but by regulatory mechanisms that involve mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt signaling pathways [12,13]. In embryogenesis, several reports indicated that IGF-I can promote preimplantation embryo development and influence cell numbers [14][15][16][17]. Moreover, a number of studies have demonstrated that IGF-I is a powerful inhibitor of apoptosis through the activation of its receptor [14,[17][18][19].…”

Optimisation of in vitro culture conditions in B6CBF1 mouse embryos

“…The application of mineral oil significantly reduced embryo development compared with the presence of paraffin oil although these two types of oil have been broadly used in embryo culture [2,10,11,37]. A recent study indicates that the use of mineral oil significantly reduces the rate of pig embryos developing to the blastocyst stage after IVF [38].…”

“…Paraffin oil [10][11][12], mineral oil [13][14][15] and silicone oil [16,17] have been broadly used to protect culture medium from evaporation and contamination when early embryos are cultured. Further studies have indicated that the application of oil affects the embryo development either in a positive or a negative way [18,19].…”

A potential use of embryonic stem cell medium for the in vitro culture of preimplantation embryos

“…For example, EGF, TGF-α, and TGF-β all promote development to the blastocyst stage, increase cell numbers [52], and stimulate trophoblast outgrowth [53]. Insulin-like growth factor 1 (IGF-1) has been shown to stimulate ICM growth in particular [54]. Furthermore, both mouse and human female reproductive tracts secrete various growth factors, such as IGF-1, EGF, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF), and the embryo itself expresses receptors for these growth factors [55][56][57][58][59][60].…”