Identification of maturation and protein synthesis related proteins from porcine oocytes during in vitro maturation

In vitro maturation (IVM) of mammalian oocytes is divided into the GV (germinal vesicle stage), MI (metaphase I stage) and MII (metaphase II stage) stages, and only fully mature oocytes have acquired the ability to be fertilized and initiate zygotic development. These observations have been mostly based on morphological evaluations, but the molecular events governing these processes are not fully understood.The aim of the present study was to better understand the processes involved in the molecular regulation of IVM using 2-DE analysis followed by mass spectrometry to identify proteins that are differentially expressed during oocyte IVM.

A total of 16 up-regulated and 12 down-regulated proteins were identified. To investigate the IVM process, we specifically focused on the proteins that were up-regulated during the MII stage when compared with the GV stage, which included PRDX 2, GST, SPSY, myomegalin, PED4D, PRKAB 1, and DTNA. These up-regulated proteins were functionally involved in redox regulation and the cAMP-dependent pathway, which are essential for the intracellular signaling involved in oocyte maturation. Interestingly, the PDE4D and its partner, myomegalin, during the MII stage was consistently confirmed up-regulation by western blot analyses.

These results could be used to better understand some aspects of the molecular mechanisms underlying porcine oocyte maturation. This study identified some regulatory proteins that may have important roles in the molecular events involved in porcine oocyte maturation, particularly with respect to the regulation of oocyte meiotic resumption, MII arrest and oocyte activation. In addition, this study may have beneficial applications not only to basic science with respect to the improvement of oocyte culture conditions but also to mammalian reproductive biotechnology with potential implications.