Stimulatory effect of insulin-like growth factor I and epidermal growth factor on the maturation of rabbit oocytes in vitro

Abstract

The effects of different combinations of epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on cumulus expansion and meiotic maturation were examined in rabbit oocytes. Selected rabbit follicular oocytes were matured in vitro and were classified as cumulus-oocyte complexes or denuded oocytes. They were cultured in TCM 199, and were treated with growth factors at different concentrations: EGF at 0, 1, 10, 50 and 100 ng ml-1, IGF-I at 0, 50, 100 and 200 ng ml-1 and EGF plus IGF-I at 10 + 50; 10 + 100; 50 + 50 and 50 + 100 ng ml-1, respectively. After 6 h of culture, the oocytes were assessed for nuclear maturation and after 16 h of culture, for cumulus expansion and maturation stage. After culture for 6 h, the incidence of germinal vesicle breakdown was higher (P < 0.05) in all of the growth factor treatments tested compared with controls. After culture for 16 h, EGF enhanced the incidence of cumulus expansion at all of the concentrations tested. Cumulus expansion was greatest with 50 mg EGF ml-1 plus 100 ng IGF-I ml-1 (72.0% versus 2.4% in controls). Treatment with IGF-I significantly increased (P < 0.05) the incidence of metaphase II stage, and maximum stimulation occurred at 100 ng IGF-I ml-1 (84.5% versus 31.1% in controls). However, IGF-I did not affect cumulus expansion. When denuded oocytes were used, no positive effects on nuclear maturation rates were observed for any treatment. These results suggest that: (1) EGF, either alone or with IGF-I, stimulates cumulus expansion; (2) the addition of IGF-I or EGF plus IGF-I significantly enhances nuclear maturation in immature rabbit oocytes; and (3) this effect is mediated by the presence of cumulus cells.

Possible Involvement of Insulin-like Growth Factor-I in Mediating the Stimulatory Effect of Recombinant Bovine Growth Hormone on Maturation of Bovine Oocytes In Vitro.

“…Although the proportion of COCs with such slightly expanded cumulus was increased with increasing concentration of the rhIGF-I, this did not necessarily correlate with the maturation rate. The poor cumulus expansion by IGF-I is also reported in bovine [4,5] and rabbit [6] COCs. Since an "expansion" factor is produced by the oocyte [34], it is assumed that IGF-I may inhibit the production of the factor by the oocyte [4][5][6].…”

“…The poor cumulus expansion by IGF-I is also reported in bovine [4,5] and rabbit [6] COCs. Since an "expansion" factor is produced by the oocyte [34], it is assumed that IGF-I may inhibit the production of the factor by the oocyte [4][5][6]. However, this assumption may not be true under the present experimental conditions because increased concentration of rhIGF-I resulted in increased, rather than decreased, proportion of COCs with slight cumulus expansion.…”

“…These supplements are known as regulators of oocyte maturation and a highly complex combination of components, and thereby it may be difficult to find direct action of IGF-I under such conditions. Using defined medium, the enhancement of maturation in only cumulus-enclosed oocytes by IGF-I was also reported in cattle [5] and rabbits [6] indicating that a possible stimulus for maturation is transferred to the oocyte via cumulus-cells. There are conflicting data on the effects of IGF-I during culture for oocyte maturation on subsequent embryonic development.…”

Effects of Phosphatidylinositol 3-Kinase Inhibitors, Wortmannin and LY294002, on Germinal Vesicle Breakdown (GVBD) in Porcine Oocytes.

“…The specific bindings of EGF to bovine and porcine cumulus cells have also been observed [28] and in general, it is accepted that IGF-I, EGF and insulin can activate PI 3-kinase in somatic cells [10,11]. More recently, Lorenzo et al [7] have reported that the addition of activator of PI 3-kinase, IGF-I, EGF or both factors, enhances GVBD and progresses to MII in rabbit oocytes via the gap junctions between the cumulus cells and oocytes in vitro. Additionally, FCS added to maturation medium, as in this study, contains IGF-I and stimulates cumulus cell expansion in porcine COCs [27].…”

The In Vitro Effect of Adiponectin on Early Bovine Embryonic Development and Transcriptomic Markers of Oocyte Competence

“…After 24 hours of in vitro maturation, the degree of cumulus expansion was scored under a stereo-microscope based on the subjective scale of 0 to 3 describe by Lorenzo et al [19], in which 0 indicates no detectable response; 1 shows the minimum observable response; 2 indicates partial expansion, with more than half of the cumulus expanded; and 3 shows full expansion, where all layers of cumulus cells have expanded, including those closest to the oocyte. Then, the oocytes were mechanically denuded of the surrounding cumulus cells using repeated pipetting in 3% sodium citrate solution and were mounted on grease-free glass slides with coverslips hold in place with a mix of vaseline and paraffin wax (20:1).…”