Mitochondria and vesicles differ between adult and prepubertal sheep oocytes during IVM.
Oocytes from prepubertal animals have a reduced ability to undergo normal embryo development and produce viable offspring. The correct quantity, activity and cytoplasmic distribution of oocyte organelles are essential for oocyte maturation, fertilisation and subsequent embryo development. The aim of this study was to quantify the ultrastructural differences between oocytes from prepubertal lamb and adult ewes using electron microscopy and stereology. We also determined whether quantitative polymerase chain reaction (qPCR) methods give comparable estimates of mitochondrial number to stereology. Mean storage vesicle volume was greater in adult compared with lamb oocytes before IVM and decreased during maturation in both adult and lamb oocytes. Mitochondrial volume and number increased in adult oocytes during maturation; however, no increase was observed in lamb oocytes. Mitochondrial DNA copy number measured by qPCR showed no differences between adult and lamb oocytes. A different distribution of mitochondria was observed in lamb oocytes before maturation, while the percentage of hooded mitochondria increased during maturation in adult oocytes and decreased in the lamb. In conclusion, the present study has identified differences in the vesicles and mitochondria between adult and lamb oocytes from ewes that may contribute to reduced developmental competence in prepubertal oocytes.
Animal Productivity, AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9053, New Zealand.
Karen L
KL
Reader
Bioinformatics and Statistics, AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9053, New Zealand.
Neil R
NR
Cox
Department of Anatomy, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
Jo-Ann L
JA
Stanton
Animal Productivity, AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9053, New Zealand.
Jennifer L
JL
Juengel
D000367:Age Factors; D000818:Animals; D004272:DNA, Mitochondrial; D047108:Embryonic Development / Q000502:physiology; D005260:Female; D059471:In Vitro Oocyte Maturation Techniques / Q000662:veterinary*; D008928:Mitochondria / Q000648:ultrastructure*; D009865:Oocytes / Q000254:growth & development / Q000648:ultrastructure*; D012756:Sheep
D004272:DNA, Mitochondrial