Role of EGF, IGF-I, sera and cumulus cells on maturation in vitro of bovine oocytes

Oral propylene glycol modifies follicular fluid and gene expression profiles in cumulus-oocyte complexes and embryos in feed-restricted heifers

Dietary supplementation with propylene glycol (PG) increases in vitro production of high-quality embryos in feed-restricted heifers. The aim of the present study was to evaluate the effects of PG in feed-restricted heifers on follicular fluid insulin and insulin-like growth factor (IGF) 1 concentrations, expression of IGF system genes in oocytes and cumulus cells and the expression of selected genes in blastocysts. Feed-restricted (R) heifers were drenched with water or PG during induced oestrous cycles (400mL of PG or water/drench, daily drenching at 1600 hours for the first 9 days of the oestrous cycle). Ovum pick-up (OPU) was performed after superovulation to produce in vitro embryos and without superovulation to recover oocytes, cumulus cells and follicular fluid. OPU was also performed in a control group (not feed restricted and no drenching). Follicular fluid IGF1 concentrations were reduced by R, and PG restored IGF1 concentrations to those seen in the control group. In cumulus cells, expression of IGF1, IGF1 receptor (IGF1R) and IGF binding protein 4 (IGFBP4) was decreased in the R group, and fully (IGF1 and IGF1R) or partially (IGFBP4) restored to control levels by PG. Blastocyst perilipin 2 (PLIN2; also known as adipophilin), Bcl-2-associated X protein (BAX), SCL2A1 (facilitated glucose/fructose transporter GLUT1), aquaporin 3 (AQP3), DNA (cytosine-5)-methyltransferase 3A (DNMT3A) and heat shock 70-kDa protein 9 (HSPA9B) expression were decreased in R heifers; PG restored the expression of the last four genes to control levels. In conclusion, these results suggest that, during follicular growth, PG exerts epigenetic regulatory effects on gene expression in blastocyst stage embryos.

Improving in vitro maturation of oocytes in the human taking lessons from experiences in animal species

One to three per cent of infertile women develop severe ovarian hyperstimulation syndrome after superovulation for assisted reproduction treatment (ART). This severe complication can be avoided when oocytes are obtained at an immature stage (germinal vesicle stage) out of small or medium-sized follicles. This hypothesis has been tested in several infertile women, but clinical pregnancies are disappointlingly low. This new approach in ART is still at an experimental phase and this treatment has still to be improved before routine clinical application. Experimental work in animals and humans suggest a beneficial effect in providing a short preliminary pretreatment with follicle-stimulating hormone to select for a developing cohort of follicles. The aspiration of oocyte cumulus complexes is carried out with a short needle applying reduced aspiration pressure. A crucial point is to provide the appropriate culture environment for the immature oocytes. An optimal cumulus-enclosed human oocyte culture system needs to be defined. The composition of the culture medium could be suggested by in vitro work carried out in animal models. As developmental competence is established during the latest phases of oocyte growth and is dependent on the storage of RNA, a prolonged in vitro maturation period (before inducing nuclear maturation) could provide the necessary transcriptional and translational changes. The conditions to achieve this improved cytoplasmic maturation by prolonging the in vitro culture remain to be defined. More objective noninvasive parameters for oocyte maturity are also needed to pursue research in this field.

A combination of EGF and IGF-I accelerates the progression of meiosis in bovine follicular oocytes in vitro and fetal calf serum neutralizes the acceleration effect

The effects of a combination of EGF and IGF-I (GFs) on the progress of meiosis and on their developmental competence were examined in cumulus-enclosed bovine oocytes. Exposure to GFs in serum-free, 0.3% PVP-containing maturation medium significantly (P<0.05) increased the frequency of oocytes with the first polar body (PB) at 16 h of culture and decreased those with PB at 20 h. The cleavage rates of PB-extruded oocytes after fertilization were not affected by treatment of GFs during maturation culture, and blastocyst yield was not improved by GFs treatment. Although replacement of PVP from GFs-containing medium with fatty acid-free BSA did not affect the timing of PB extrusion, replacement with 10% FCS neutralized the acceleration effects of GFs. Replacement for macromolecule in maturation medium did not improve blastocyst yield of PB-extruded oocytes after fertilization. These results indicate that the progression of meiosis in bovine oocytes with cumulus cells is accelerated by exposure to GFs in serum-free maturation medium but their developmental competence is not improved, and that the acceleration effects on the progress of meiosis is neutralized by the presence of FCS in maturation medium with no improvement of developmental competence after in vitro fertilization.

Influence of vasoactive intestinal peptide (VIP), atrial natriuretic peptide (ANP) and insulin-like growth factor-I (IGF-I) on in vitro maturation of prepubertal and adult sheep oocytes

Much effort has been focused on establishing optimal conditions for obtainingin vitromaturation of oocytes from different species with results comparable to those achieved afterin vivodevelopment (reviewed by Brackett, 1992). However, even though extraordinary progress has been made, thein vitrotechnology for oocyte maturation lags far behind thatin vivoand improvements are needed to increase the quantity and quality of the embryos produced from these matured oocytes.