Improvement of the Developmental Ability of Nuclear Transfer Embryos by Using Blastomeres from In Vitro Fertilized Embryos Selected According to the Early Developmental Stage and Cell Division Status as Donor Cells in Cattle

Abstract

Abstract. This study was conducted to improve the developmental ability of nuclear transfer (NT) embryos by using blastomeres from in vitro fertilized (IVF) embryos with high quality as donor cells. The IVF embryos selected at the 2-cell stage at 24-h postinsemination (hpi) and again at the ≥8-cell stage at 48 hpi (Selected-IVF-embryos) showed the highest blastocyst formation rate among embryos. When blastomeres from the Selected-IVF-embryos (Selected-NT group) or Nonselected-IVF-embryos (Non-selected-NT group) were used as donor cells for NT, the blastocyst formation rate in the Selected-NT group (25.6%) was significantly higher than that in the Non-selected-NT group (13.5%). When blastomeres from the Selected-IVF-embryos at 108 (contained many cells before cell division) and 126 hpi (contained many cells immediately after cell division) were used as donor cells for NT (108-and 126-NT groups, respectively), the 126-NT group showed a significantly higher blastocyst formation rate (32.1%) than the 108-NT group (16.8%). Embryo transfer of blastocysts in the 126-NT group showed that 11 of 23 recipients became pregnant; nine calves were obtained. For the NT embryos reconstructed using in vivo derived embryos, 9 of 20 recipients became pregnant; seven calves were obtained. These results indicate that the blastocyst formation rate of NT embryos can be improved by using blastomeres from IVF embryos selected at the early developmental stage, especially immediately after cell division, and that the resultant NT embryos have a high developmental ability to progress to term that is comparable to NT embryos reconstructed using in vivo derived embryos. Key words: Bovine, Embryo, In vitro fertilization, Nuclear transfer (J. Reprod. Dev. 57: [249][250][251][252][253][254][255] 2011) uclear transfer (NT) technologies are now widely used by numerous laboratories to produce clone animals from embryonic and somatic cells. However, the overall efficiency of clone animal production is influenced by the different sources of donor cells; early pregnancy losses of cattle established from somatic nuclear transfer (sNT) are commonly above 50% [1,2], and the frequency of early fetal mortality is about two times higher with sNT than with embryonic nuclear transfer [3]. Therefore, it can be expected that a higher proportion of transferred NT embryos reconstructed from less-differentiated embryonic blastomeres would result in viable offspring compared with sNT. In addition, the production of embryonic cloned calves is permitted in Japan and food products derived from NT cattle can be on the market, thereby increasing commercial acceptance of the technology. Furthermore, the use of blastomeres from the same embryos for nuclear transfer to produce numerous identical bovine offspring is of great value for multiplication of genotypes having a superior economic value and is expected to contribute to their genetic improvement.In NT technology using embryos at an early developmental stage as donor cells, in vitro fertilized (IVF) embryos are oft...

Breed influences on in vitro development of abattoir-derived bovine oocytes

“…In general, early development is believed to be an indicator of good developmental ability in bovine in vitro embryo production [32-34], a concept that was contradicted by the final blastocyst rate in this study since the SH group had the lowest blastocyst rate on day 8. It is possible that the SH group suffered from an extensive 8 - 16 cell block but since only blastocysts were assessed after culture, the main point of developmental arrest is not clear.…”