Research and issues for pregnancy improvements during the peri-implantation period in ruminants

哺乳類の妊娠・着床期において，受精卵の約半数は子宮へ着床する前に死滅してしまい，妊娠は成立しない．この早期胚死滅により，人工授精などの技術の向上にも関わらず，肉用牛，乳用牛とも受胎率は停滞/低下が続いている．反芻動物の着床期には，胚・栄養膜細胞からインターフェロン・タウ（IFNT）が子宮腔内へ分泌されることにより黄体退行が抑制され，さらに母体と胚の成長が同調し，妊娠が成立する．IFNTを利用することで，早期胚死滅を防ぎ，受胎率向上が望めると期待されており，研究が進められてきた．IFNTの発現制御に関与する因子は多数見つかっており，また，IFNTの子宮内投与等の応用研究も行われているが，未だ実用化には至っていない．今後は，受胎率改善を目指すにあたり， in vivoの胚がどのような条件でIFNTを適切に発現し得るか，すなわち栄養膜細胞においてIFNTの発現をはじめ，その上流や周辺で起こるべき現象を広い視点で捉えることが必要であろうEven after successful fertilization in the mammalian species, nearly 50% of pregnancies fail, 70∼80% of which are lost during the peri-implantation period. It is thought that early embryonic loss results from a lack or shortage of pregnancy recognition. In ruminants, interferon tau (IFNT), an anti-luteolytic substance produced by the embryonic trophectoderm, is a major signal for the maternal recognition of pregnancy. For over 10 years, we have been studying molecular mechanisms associated with IFNT gene transcription for its effective regulation, resulting in the identification many regulatory factors. In addition, intrauterine administration of IFNT has been performed for the means to improve pregnancy rate. However, no effective therapy with IFNT is yet known to exist. For these reasons, future research needs to be directed toward the identification of what conditions that allows the conceptus to express IFNT as well as other factors properly in vivo. More importantly, these findings should be placed into the practical use in which the treatment developed actually improves pregnancy rates