During fertilization, the sperm triggers resumption from the arrest, extrusion of the second polar body and pronuclear formation whose events are collectively acknowledged as ‘oocyte activation‘. In mammalian species up to date, oocyte activation requires fertilization-associated increases in the intracellular concentration of calcium. These periodical rises are referred to as calcium oscillations. Result studies suggest that these calcium oscillations have important role in not only oocyte activation but also development of mammals. We focus on two molecules, phospholipase C zeta (PLCζ;) and inositol 1,4,5-triphosphate receptor (IP₃R) which have important role in regulation of calcium oscillations during fertilization in mammals. In this review, we will discuss present status and future perspective of molecular mechanism during fertilization in mammals.

Intracellular distribution of mitochondria varies during development of the oocyte into a fertilizable egg. Here we demonstrate a change in the distribution of mitochondria during oocyte growth and maturation in living mouse oocytes. In growing oocytes, mitochondria concentrated into subcortical and perinuclear areas, whereas it diffusely distributed throughout the cytoplasm in fully-grown oocytes, indicating the variation of mitochondrial distribution in the same G2/M cell-cycle stages. GFP-labeled mitochondria reveal that oocyte maturation involves dynamic reorganization of the mitochondria, and whose process is associated with microtubule organization. These spatio-temporal regulations of mitochondria in oocytes may be important process in the preparation of fertilization and subsequent embryonic development.

Metabolic state during oogenesis and embryogenesis is so tightly regulated with dynamic changes in metabolic substrates and pathways, that its dysregulation causes detrimental effects on oocytes and preimplantation embryos, and may further affect postnatal physiological states and/ or susceptibility to adult metabolic diseases. It is well known that mitochondria, as major sites of energy production and reactive oxygen species, a by-product of oxidative phosphorylation, are much responsible for metabolism. Recently, it has been revealed that quite a lot of mitochondrial proteins are acetylated and thereby regulated in their functions. Most of them are involved in many metabolic pathways, suggesting that protein acetylation is also an important modification in embryogenesis. Recent studies have also elucidated that the mitochondrial protein deacetylation process mostly depends on certain members of the sirtuin family, a NAD dependent deacetylase family, that are involved in a variety of (patho) physiological events such as tumorigenesis and metabolic disorders. This article reviews recent and current studies of mitochondrial functions in early embryos and their regulatory mechanisms, focusing on mitochondrial protein deacetylation by the sirtuin family.

Oocyte quality impacts early embryonic survival and the establishment and maintenance of pregnancy. The cellular and molecular basis assessments of oocyte quality may be regarded as potential predictors of oocyte developmental competence. However, these methods are invasive and therefore have no value as prediction tools in Assisted Reproductive Technology. On the other hand, we developed a novel cell respiration measuring system, scanning electrochemical microscopy (SECM). This measuring system is able to determine the respiratory activity of individual embryos non-invasively and quantitatively. Therefore, the SECM may be useful to assess the quality of embryos and oocytes in mammals. In the present review, we describe the SECM procedures briefly and our analysis of respiratory activity in the porcine oocytes using by the SECM.

To establish a new model for the selection of a single blastocyst that has high developmental potential, the relationship between the developmental competence of blastocysts and their oxygen consumption was assessed. The oxygen consumption rate of blastocysts just after thawing was significantly lower than that of non-frozen blastocysts. The oxygen consumption of blastocysts with high developmental competence was restored earlier than that of blastocysts with low developmental competence in spite of the absence of differences in morphology. Our data suggest a new model for the selection of frozen-thawed blastocyst with high developmental competence based on its cellular respiration activity.

The stainability of mouse embryos with brilliant cresyl blue (BCB) and the development to blastocysts of BCB-positive and BCB-negative embryos were examined. From the 2-cell to the morula stages, the incidences of BCB-positive embryos collected from mature mice were 94.2 to 96.4%. These rates were significantly higher at all stages than those of BCB-negative embryos. The rates of development to blastocysts of BCB-positive embryos (85.7 to 96.7%) were significantly higher than those of BCB-negative embryos (0 to 50.0%) at all stages. In 2-cell embryos and morulae collected from aged mice, the incidences of BCB-positive embryos (79.5 and 58.6%) were significantly higher than those of BCB-negative embryos (20.5 and 41.4%, respectively). The rates of development to blastocysts of BCB-positive 2-cell embryos and morulae collected from aged mice were 77.1 and 79.4%, which were significantly higher than those of BCB-negative embryos, 0 and 45.8%, respectively. Although the incidences of BCB-positive embryos collected from aged mice were significantly lower than those collected from mature mice, the rates of development to blastocysts in BCB-positive embryos did not differ between the embryos collected from aged and mature mice. In these findings, we demonstrate that BCB-positive embryos have high developmental ability to the blastocyst stage. A correlation was also found between BCB stainability and G-6-PDH activity in mouse eggs and embryos.

An outpatient service in which an embryologist provides information was started at our clinic. Eighty-five patients visiting our clinic were asked to complete a questionnaire on 1) patient's status, 2) age, number of oocyte retrievals and number of outpatient visits, 3) time for consultation, 4) questions asked by the patient, 5) understanding of information, and 6) satisfaction with responses to requests. The results were as follows; 1) 56.7%, 41.7% and 1.7% of the patients were wife only, husband and wife, and husband only, respectively; 2) average age of the wives was 37.6 years, average number of oocyte retrievals was 3.7 and average number of outpatient visits was 1.1; 3) average times for consultation were 41.3 min, 41.7 min and 20 min for wife only, husband and wife, and husband only respectively; 4) questions on fertilized ova, future treatment, past treatment, and semen findings were asked by 43.1%, 17.6%, 9.8% and 9.8% of the patients, respectively; 5) all of the patients understood well or fairly well; and 6) responses were sufficient, reasonably sufficient and insufficient for 73.3%, 23.3% and 3.3% of the patients, respectively. Services providing information by embryologists are good opportunities for embryologists to understand patients' feelings.