Mitochondrial distribution, ATP-GSH contents, calcium [Ca2+] oscillation during in vitro maturation of dromedary camel oocytes

Abstract

Dromedary camel oocytes have the ability to spontaneous parthenogenetic activation and development in vivo and in vitro. The present study was conducted to investigate changes in mitochondrial distribution, adenosine triphosphate (ATP), and glutathione (GSH) contents and [Ca2+] oscillation during in vitro maturation and spontaneous parthenogentic activation of dromedary camel oocytes. Dromedary camel cumulus-oocyte complexes (COCs) were matured in TCM199 medium supplemented with 10% FCS + 10 μg/mL FSH + 10 IU hCG + 10 IU eCG + 10 ng/mL EGF and 50 μg/mL gentamycine. Maturation was performed at 38.5 °C under 5% CO2 in humidified air for 40 h. After maturation and removal of cumulus cells, oocytes were classified into: immature cultured (Group 1); metaphase II (M II, Group 2); and spontaneously parthenogenetically activated (with 2 polar bodies, Group 3); cleaved embryos (Group 4); and immature oocytes served as a control (Group 5). Cytoplasmic mitochondrial distribution, ATP-GSH contents, calcium [Ca2+] oscillation were determined. Results indicated that M II and spontaneously parthenogenetically activated oocytes represent 37.53% and 32.67% of the cultured oocytes, respectively, and 3.3% cleaved and developed to 2-16-cell stage embryos. Mitochondrial distribution, ATP-GSH contents and [Ca2+] oscillation were significantly (P < 0.01) differ between immature and matured dromedary camel oocytes. Mitochondrial distribution showed clustering form in matured oocytes without polar body. High polarized mitochondrial distribution (HPM) was detected in M II and spontaneously parthenogenetically activated oocytes, and the intensity of MitoTracker Red was higher in spontaneously parthenogenetically activated than M II. ATP-GSH contents and the duration of [Ca2+] oscillation were significantly (P < 0.01) higher in spontaneously parthenogenetically activated than M II oocytes or that matured without polar body. In conclusion, the higher incidence of spontaneously parthenogenetically activated in vitro matured dromedary camel oocytes could be attributed to the high polarized mitochondrial distribution associated with significantly higher ATP-GSH contents and duration of [Ca2+] oscillation.