Beta-catenin localization and timing of early development of bovine embryos obtained from oocytes matured in the presence of follicle stimulating hormone.

In mammalian species, embryos which grow more rapidly are believed to be more competent and viable than they are slower developing counterparts. Although the most important decrease in development occurs between the zygote and blastocyst stages, there is a growing amount of evidence to suggest that maturation conditions and oocyte quality have a profound influence on the developmental potential of early mammalian embryos. Gene transcripts and polypeptides stored in the oocytes, such as junctional proteins, sustain the initial development of embryos. In the present study we demonstrated a relationship between the timing of the development of in vitro-produced bovine embryos and the distribution and localization of the junctional protein beta-catenin. We further demonstrated that the presence of FSH during IVM supports cleavage and the blastocyst rate, and also has a positive effect on the speed of development, since embryos obtained from oocytes matured with the gonadotropin and observed on days 4, 5 and 6 post-insemination (p.i.) grew faster than those matured in a medium supplemented with BSA. Moreover, the majority of embryos which developed past the 16-cell stage showed a proper distribution of beta-catenin just beneath the membrane surfaces of all blastomeres and an appropriate morphology, as confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis. In conclusion, our data suggest that supplementing FSH during in vitro maturation aids the development of bovine embryos and promotes the correct expression of beta-catenin, increasing the likelihood that embryos will develop to the blastocyst stage.

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