Optimization of DNA counterstaining for methylation and hydroxymethylation immunostaining in bovine zygotes

Abstract

The review presents an overview of studies that examined the effects of follicular aging and maternal aging in the bovine model. The first of three main sections is a discussion of the developmental competence of oocytes from (1) the ovulatory follicle of 2-wave and 3-wave estrous cycles, (2) dominant follicles that develop under high or low LH pulse frequency, and (3) natural versus FSH-stimulated ovulatory follicles. The second section highlights the effects of maternal aging. Maternal aging in cattle is associated with (1) elevated circulating FSH concentrations, (2) reduced response to superstimulatory treatment, and (3) markedly decreased early embryonic development in cows >12 year of age. The third and final section on superstimulation protocols addresses the effects of the duration of FSH stimulation and withdrawal (i.e., FSH “starvation” or “coasting”) on oocyte competence. Ovarian superstimulation for 4 days altered the expression of genes related to angiogenesis, and activated oxidative stress-response genes. Extending the duration of FSH stimulation from 4 to 7 days resulted in a greater and more synchronous ovulatory response and optimal oocyte maturation. The highest rates of blastocyst development in vitro were obtained when FSH support was discontinued for 44 to 68 h and granulosa cell SMAD7 mRNA was predictive of this period. Longer periods of FSH starvation resulted in a loss of oocyte competence or ovulatory capability. By extending the bovine model to the transcriptome level, new approaches and treatments may be devised to resolve subfertility in women and animals.