Dielectrophoretic behavior of in vitro-derived bovine metaphase II oocytes and zygotes and its relation to in vitro embryonic developmental competence and mRNA expression pattern

Selecting developmentally competent oocytes and zygotes based on their morphology is more often influenced by personal judgments and lacks universal standards. Therefore, this experiment was conducted to investigate the rate of development and mRNA level of dielectrophoretically separated oocytes and zygotes to validate dielectrophoresis (DEP) as non-invasive option for selection of oocytes and zygotes. In the first experiment, metaphase II oocytes with (PB(+)) and without (PB(-)) first polar body and zygotes were subjected to DEP at 4 MHz and 450 mum electrode distance and classified into fast, very fast, slow, and very slow depending on the time elapsed to reach one of the electrodes in the electric field. Parthenogenetic activation was employed to monitor the embryonic development of dielectrophoretically classified oocytes. The result revealed that at 6 and 7 days of post-activation, the blastocyst rate of very slow dielectrophoretic PB(+) and PB(-) oocytes was significantly (P < 0.05) lower than other groups. Similarly, in zygotes, the blastocyst rate at 7 days post-insemination was higher (P < 0.05) in the very fast dielectrophoretic categories when compared with the slow and very slow categories. In the second experiment, mRNA level was analyzed in the very fast and very slow dielectrophoretic PB(+) oocytes and zygotes respectively using the bovine cDNA microarray. The result showed that 36 and 42 transcripts were differentially regulated between the very fast and very slow dielectrophoretic categories PB(+) oocytes and zygotes respectively. In conclusion, dielectrophoretically separated oocytes and zygotes showed difference in the rate of blastocyst development accompanied by difference in transcriptional abundances.