Developmental capacity, energy metabolism and ultrastructure of mature oocytes from prepubertal and adult sheep

Abstract

Development to the blastocyst stage was assessed for oocytes obtained from prepubertal and adult sheep matured and fertilized in vitro. The proportion of cleaved oocytes reaching the blastocyst stage was significantly lower for oocytes derived from prepubertal sheep than for those from adult sheep (7.4% and 24.6% respectively). There were no differences in the metabolism of glucose, glutamine or pyruvate between oocytes matured in vivo and in vitro, or of glucose or pyruvate between oocytes from prepubertal and adult sheep. Glutamine metabolism by mature oocytes from prepubertal sheep was significantly lower than that by oocytes from adult sheep. Ultrastructural studies revealed no differences in the morphology of cytoplasmic organelles of oocytes matured in vitro from prepubertal and adult sheep, but differences in the volume fraction and size of mitochondria and cortical granules were observed. These data suggest that mature oocytes from prepubertal sheep do not possess the developmental potential of their adult-derived counterparts, and this phenomenon may be associated with metabolic and ultrastructural anomalies.