Nonetheless, caution should be exercised in assessing the potential role and regulation of ovarian prohi-bitin expression, because measuring total prohibitin content may have limited physiologic significance. Potentially, the acidic isoform of the protein could well be the active form of prohibitin. Currently, we are investigating the site of phosphorylation of prohibitin using high-performance liquid chromatography/mass spectrometry techniques. The accumulation of prohibitin was observed in the aberrant embryos after NT and IVF followed by heat shock.
Whereas cytoplasmic fragmentation and developmental arrests are common in mammalian preimplantation embryos raised in vitro, they may not always be paralleled by immediate activation of the obligatory apoptotic pathways. Both apoptotic and antiapoptotic molecules are expressed by the embryo undergoing fragmentation, yet such embryos do not appear to die quickly and may not show signs of nuclear DNA fragmentation until several days after embryonic cleavage-arrest. Such a paradox could be explained by a dual role of prohibitin as an antiproliferative and cell survival factor, which could prevent further cleavage of defective embryos and delay activation of the apo-ptotic pathways in the arrested embryos, respectively.