Chromatin Configuration Within the Germinal Vesicle of Horse Oocytes: Changes Post Mortem and Relationship to Meiotic and Developmental Competence1

Abstract

We evaluated the relationship of initial chromatin configuration to time of oocyte recovery and to nuclear maturation after culture in horse oocytes having compact (Cp) and expanded (Ex) cumuli. In addition, we evaluated the effect of oocyte type, time of recovery, and duration of culture on blastocyst development after intracytoplasmic sperm injection. In oocytes collected within 1 h of slaughter, fibrillar and intermediate chromatin configurations were more prevalent in Cp than in Ex oocytes (68% and 12%, respectively). In Cp oocytes collected after a 5- to 9-h delay, the proportions in the fibrillar and intermediate configurations decreased significantly, and the proportions of degenerating and homogeneously fluorescent configurations increased. When cultured, 20% of oocytes classified as having fibrillar chromatin resumed meiosis, whereas 82% of intermediate and 81% to 86% of condensed chromatin oocytes did so. Meiotic resumption was higher in oocytes recovered immediately after slaughter, but these oocytes took longer to mature. Duration of maturation significantly affected blastocyst development rates in Cp oocytes recovered after a delay (13% and 38% for oocytes matured 24 and 36 h, respectively). Oocytes recovered after a delay had higher blastocyst development rates than did those collected immediately after slaughter. We conclude that the fibrillar and intermediate chromatin configurations may degenerate during ovary storage, resulting in decreased maturation rates, especially of Cp oocytes. Time of oocyte recovery and duration of maturation significantly affect the rate of blastocyst development. Oocytes with Cp and Ex cumuli have similar developmental competence to the blastocyst stage.

In Vitro Development of Equine Oocytes from Preserved Ovaries after Intracytoplasmic Sperm Injection

“…In the present study, we stored equine ovaries at 15 to 20 C and successfully cultured the oocytes to the blastocyst stage (25.5%). Our results were comparable with other recent studies that achieved blastocyst rates of 27-39% after ICSI using ovaries preserved for 3-9 h [11][12][13]. These results indicate that the immature horse oocytes from ovaries preserved for one day retained their in vitro developmental competence.…”

“…Recently, several studies have shown that blastocyst formation rates of 27-39% can be obtained by in vitro culture (IVC) following ICSI of equine oocytes from ovaries preserved for 3-9 h [11][12][13]. However, up to now, there have been few reports about the effect of storage of ovaries for one day on subsequent embryogenesis in the horse.…”

OMICS for the Identification of Biomarkers for Oocyte Competence, with Special Reference to the Mare as a Prospective Model for Human Reproductive Medicine

“…Horses make a valuable model for oocyte assessments associated with penetration of the zona pellucida (e.g. PB biopsy) because, in contrast to species such as cattle and sheep, methods for fertilization via intracytoplasmic sperm injection (ICSI) are well established in the horse (Hinrichs et al, 2005;Choi et al, 2006). Sperm injection is necessary to achieve fertilization after penetration of the zona pellucida for investigative p u r p o s e s , a s t h e d e f e c t i n t h e z o n a w o u l d l e a d t o p o l y s p e r m y i f s t a n d a r d i n v i t r o fertilization (IVF) were to be performed.…”

Maternal age and in vitro culture affect mitochondrial number and function in equine oocytes and embryos

“…Despite the relatively low per oocyte success rates (18%-36% of recovered oocytes develop into a transferable blastocyst; Hinrichs et al 2005;Galli et al 2007), during the past 5 years IVP has become a commercially viable means of breeding horses. The increasing popularity of IVP despite the relatively high costs is explained by the number of transferable blastocysts per ovum pick-up (OPU) session (0.6-0.8; Galli et al 2014), which compares favourably with embryo flushing in the field.…”