Research Topics

Our assisted reproductive medicine unit was established in 2018. We focus on various methods of assisted reproductive technology including in vitro maturation (IVM), in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), the cryopreservation of embryos, oocytes and sperm, and embryo selection. At the same time, we also aim to achieve a greater understanding of certain unknown mechanisms of meiosis, fertilization and embryo development in human.

The meiotic abnormalities in human oocytes and their mechanisms

During the maturation process of human oocytes, numerous genes are responsible for meiosis. Recent studies have begun to reveal that defects in some interrelated genes are the cause of female infertility. In our laboratory. We aim to perform functional analyses of the process of oogenesis, during the first and second meiosis using oocytes from mutant mice, which present with a mutation, leading to genetically developed abnormalities on chromosomal crossing-over during meiosis. In this way, we hope to contribute to the existing body of therapeutic strategies and preventive measures which can be taken against human infertility. * This study is a collaborative work with the unit of Applied Animal Genetics at Okayama University.

The elucidation of the mechanism of dysmorphic phenotypes in human oocytes and preventive measures against those dysmorphisms

The dysmorphic phenotypes to be found in human oocytes are unlike any other species, with the exception of chimpanzee oocytes. Among these dysmorphisms, we have been focusing on two phenotypes: smooth endoplasmic reticulum clusters (sERCs) and refractile/lipofuscin bodies. We have found that the incidence of mitotic and meiotic cleavage failure during the second polar body extrusion is significantly higher in oocytes with sERCs than that in oocytes without sERCs. Regarding the refractile body (RB), we have reported that it presents with autofluorescence. Viewed by means of transmitted electron microscopy, the refractile bodies display the conventional morphology of lipofuscin inclusions and consist of a mixture of lipids and dense granule materials. We aim to elucidate the mechanisms of these dysmorphic phenotypes in human oocytes and work towards preventive measures against them. * This study is a collaborative work with the Okayama University Hospital and Fertility clinics.

Research on the Mechanism of Oocyte Development

Folliculogenesis is the process in which a recruited primordial follicle develops into a preovulatory follicle. This long process highlights the importance of signaling between the oocyte and the surrounding somatic cells. Our research is focused on the mechanism of oogenesis/folliculogenesis in human and animal ovaries. In the future, we believe that the establishment of oogenesis/folliculogenesis in in vitro culture may contribute to the improvement of assisted reproductive medicine, animal reproduction, and the conservation of endangered species.

Publication List

Assoc. Prof. OTSUKI Junko

• Okajima N, Xiao, W, Lopata A, Sankai T, Yasmin L, Nagai Y, Okamoto R, Tasaki H, Otsuki J. Nuclear to cytoplasmic ratios of 1PN and 2PN zygotes in the mouse. Zygote. 2021 impress
• Otsuki J, Iwasaki T, Enatsu N, Katada Y, Furuhashi K, Shiotani M. The inclusion of blastomeres into the inner cell mass in early-stage human embryos depends on the sequence of cell cleavages during the fourth division. PLoS One. 2020 Oct 19;15(10):e0240936. doi: 10.1371/journal.pone.0240936.
• Hayashi N, Enatsu N, Iwasaki T, Otsuki J, Matsumoto Y, Kokeguchi S, Shiotani M. Predictive factors influencing pregnancy rate in frozen embryo transfer. Reprod Med Biol. 2020 Mar 11;19(2):182-188. doi: 10.1002/rmb2.12322.
• Otsuki J, Iwasaki T, Enatsu N, Katada Y, Furuhashi K, Shiotani M. Noninvasive embryo selection: kinetic analysis of female and male pronuclear development to predict embryo quality and potential to produce live birth. Fertil Steril. 2019 Nov;112(5):874-881. doi: 10.1016/j.fertnstert.2019.07.015.
• Takahashi H, Otsuki J, Yamamoto M, Saito H, Hirata R, Habara T, Hayashi N. Clinical outcomes of MII oocytes with refractile bodies in patients undergoing ICSI and single frozen embryo transfer. Reprod Med Biol. 2019 Nov 25;19(1):75-81. doi: 10.1002/rmb2.12305.
• Saito H, Otsuki J, Takahashi H, Hirata R, Habara T, Hayashi N. A higher incidence of smooth endoplasmic reticulum clusters with aromatase inhibitors. Reprod Med Biol. 2019 Sep 11;18(4):384-389. doi: 10.1002/rmb2.12296.
• Otsuki J, Iwasaki T, Katada Y, Tsutsumi Y, Tsuji Y, Furuhashi K, Kokeguchi S, Shiotani M. A higher incidence of cleavage failure in oocytes containing smooth endoplasmic reticulum clusters. J Assist Reprod Genet. 2018 May;35(5):899-905. doi: 10.1007/s10815-018-1119-3.
• Tsuji Y, Otsuki J, Iwasaki T, Furuhashi K, Matsumoto Y, Kokeguchi S, Shiotani M. Retrospective comparative study of the factors affecting birthweights in frozen-thawed embryo transfer, compared to fresh embryo transfer. Reprod Med Biol. 2017 Jun 28;16(3):283-289. doi: 10.1002/rmb2.12038.
• Otsuki J, Iwasaki T, Tsuji Y, Katada Y, Sato H, Tsutsumi Y, Hatano K, Furuhashi K, Matsumoto Y, Kokeguchi S, Shiotani M. Potential of zygotes to produce live births can be identified by the size of the male and female pronuclei just before their membranes break down. Reprod Med Biol. 2017 Apr 12;16(2):200-205. doi: 10.1002/rmb2.12032.
• Otsuki J, Iwasaki T, Katada Y, Sato H, Furuhashi K, Tsuji Y, Matsumoto Y, Shiotani M. Grade and looseness of the inner cell mass may lead to the development of monochorionic diamniotic twins. Fertil Steril. 2016 Sep 1;106(3):640-4. doi: 10.1016/j.fertnstert.2016.05.007.



Asst. Prof. TASAKI Hidetaka

• Munakata, Y., Kawahara-Miki, R., Shiratsuki, S., Tasaki, H., Itami, N., Shirasuna, K., Kuwayama, T. & Iwata, H. Gene expression patterns in granulosa cells and oocytes at various stages of follicle development as well as in in vitro grown oocyte-and-granulosa cell complexes. J Reprod Dev. 2016 Aug 25;62(4):359-66. doi: 10.1262/jrd.2016-022.
• Oi, A., Tasaki, H., Munakata, Y., Shirasuna, K., Kuwayama, T. & Iwata, H. Effects of reaggregated granulosa cells and oocytes derived from early antral follicles on the properties of oocytes grown in vitro. J Reprod Dev. 2015;61(3):191-7. doi: 10.1262/jrd.2014-123.
• Tasaki, H., Iwata, H., Sato, D., Monji, Y. & Kuwayama, T. Estradiol has a major role in antrum formation of porcine preantral follicles cultured in vitro. Theriogenology. 2013 Mar 15;79(5):809-14. doi: 10.1016/j.theriogenology.2012.12.009doi: 10.1016/j.theriogenology.2012.12.009.