Cumulus cell and oocyte mRNA expression of hormone and growth factor receptors in mares

Abstract

determined in old mares, but could represent a cause of age-associated early embryo loss. We hypothesized that alterations in the meiotic spindle and chromosomal alignment occur more frequently in the oocyte of old versus young mares. Oocytes were collected from the dominant follicles of young (4-11 yr, n 1⁄4 7) and old ( 20 yr, n 1⁄4 8) estrous mares and fixed at 44 h after administration of a GnRH analog to the donor. Oocytes were stained for DNA (Hoechst 33258) and microtubules (mouse anti a and b tubulin and goat anti-mouse-alexa488). Confocal images of the oocytes' meiotic spindles were analyzed to determine spindle integrity and alignment of chromosomes. Spindle conformation was considered normal when the following criteria were observed: bipolar organization, microtubules converging at both poles, and chromosomes evenly aligned at the equatorial plate. Atypical meiotic spindle morphology was observed in more oocytes from old versus youngmares (7/8 and 0/7, respectively; P< 0.05, Fisher's Exact Test), with oocytes from old mares having normal chromosomal alignment (n 1⁄4 1), nonaligned chromosomes (n 1⁄4 5), or a disarrangement of the spindle (n 1⁄4 2). Results of our study support that advanced mare age is associated alterations in morphology of the meiotic spindle and an increase in misalignment of chromosomes, which could affect embryo viability and developmental competence.