278 GENE EXPRESSION PROFILE OF OVINE OOCYTES AND CUMULUS CELLS WITH REFERENCE TO PREMATING NUTRITION

Abstract

Previous studies on sheep have demonstrated effects of maternal nutrition on fetal development with effects being observed on reproductive function (Rae et al. 2002 Anim. Reprod. Sci. 72, 63–71), blood pressure (Gopalakrishnan et al. 2004 Am. J. Physiol. Regul. Integr. Comp. Physiol. 287, R12–R20), and behavior (Erhard et al. 2004 Behav. Brain Res. 151, 25–35) in the adult offspring. It is known that gene expression in developing oocytes and very early embryos is influenced by their environment and some of the effects of nutrition on reproductive and other systems are likely to be expressed through such early changes (Hyttel 2000 Anim. Reprod. Sci. 60–61, 49–60). Effects of nutrition on oocyte function (i.e. before ovulation and fertilization) and resultant embryo quality have been observed (Gonzalez-Bulnes et al. 2004 Reprod. Fertil. Dev. 16, 421–435), but effects on oocyte gene expression have not been investigated. The aim of the present study was to investigate the effects of premating nutrition on the expression of selected genes in sheep cumulus cells and oocytes. For this purpose, 16 cast age ewes of proven fertility were used. At the time of manipulation and study, all ewes had a condition score of approximately 2.5. During the 2 weeks before slaughter, ewes of one group were fed a ration providing 0.5-live weight (n = 10) maintenance requirements and the other group 1.5-live weight (n = 6) maintenence requirements. This treatment ensured that all animals had similar numbers of potentially ovulatory follicles but different patterns of ovarian follicle maturation and, accordingly, different numbers of follicles and oocytes undergoing the final stages of maturation. The ewes's reproductive cycles were synchronized using intravaginal pessaries inserted 2 weeks before slaughter. At slaughter, ovaries were recovered and oocytes and associated cumulus cells were aspirated from all follicles >2 mm in diameter. For each ovary, oocytes derived from follicles with a diameter <4 mm and >4 mm were pooled separately, and stored for further analysis. Associated cumulus masses were collected and stored singly for subsequent investigations. As expected from previous observations, the number of visible follicles, the ratio of small-to-large antral follicles, and the total numbers of oocytes per ewe were similar for control and underfed ewes. Furthermore, the expression levels of the markers for oocyte growth, GDF-9, BMP-15, and c-kit, were investigated. Data were analyzed by ANOVA followed by Duncan test. Results showed no major differences between groups, independent of follicle diameter. These data suggest that the nutritional status of donor ewes did not significantly affect the expression profiles of these genes. However, further analyses on a greater panel of genes is required to rule out premating nutrition effects on oocyte gene expression. Furthermore, effects on the cumulus cell gene expression profile remain to be investigated.

This work was supported by the University of Milan, FIRST 2006; Scottish Executive Environment and Rural Affairs Department.