Relationships of Ca2+ Oscillations and ER Cluster Distribution to Porcine Oocyte Fragmentation

Ca2+ is an important intracellular messenger during oocyte development. Ca2+ oscillations are dependent upon the Endoplasmic Reticulum (ER), an internal Ca2+ store capable of releasing and re-sequestering Ca2+. However, mechanisms that regulate oocyte fragmentation are unclear. The aim of the current study was to investigate the mechanism of Ca2+ release and ER cluster distributions during fragmentation of aging culture porcine oocytes. After oocytes were cultured over a 40 h interval, ER cluster distributor and Ca2+ amplitudes significantly decreased. Oocyte fragmentation appeared after cells had been cultured 24 h and reached its peak at 48 h. At 40 h, normal morphology oocytes (NMor) had low Ca2+ amplitude and little ER cluster distributor; partial fragmentation (PFra) oocytes had less frequent and shorter amplitudes of Ca2+ release with ER cluster distribution partly aggregated in cytoplasm; whereas complete fragmentation oocytes (Cfra), which were increased by low voltage EA or enucleation, had no Ca2+ amplitude or ER cluster distribution. The number of PFra oocytes that proceeded to CFra following aging was increased in a Ca2+ free medium. We therefore conclude that extracellular Ca2+ abnormality resulted in altered intracellular Ca2+, leading to changes in oocyte fragmentation dynamics.