The volume density of total mitochondria was greater for embryos from the in vivo, IVPSR, and mSOF treatments than for those from the IVPS treatment. This resulted, in part, from the increased volume density of immature mitochondria in compact morulae produced in the serum-restricted and the serum-free treatments compared with those from the IVPS treatment. Immature mitochondria are organelles that have few, peripherally localized cristae. In primate embryos, this type of mitochondrion has been noted as typically found during the early cleavage and morula stages of development. Because immature mitochondria have fewer cristae, they may also have a decreased ability to metabolize lipid and produce ATP.
Cell death occurs as a normal part of in vivo embryo development. In the primate, vacuolated mitochondria have been associated with the degeneration of aging oocytes and subsequent cell death. In the present study, no differences were found in the volume density of vacuolated mitochondria for embryos from the four treatment groups. In addition, no differences were found among treatments in the volume densities of other organelles typically associated with cell degeneration including inclusion bodies, apoptotic bodies, or debris. Dead or dying cells have been found in otherwise normal primate preimplantation stage embryos produced in vivo. Thus, it appears that production of compact morulae in vitro did not contribute to an increase in the occurrence of cell death compared with that found in embryos produced in vivo.