Transplantation of Adult Fibroblast Nuclei into the Central Region of Metaphase II Eggs Resulted in Mid-Blastula Transition Embryos

Recently, a novel technical method to perform somatic nuclear transplantation (NT) in zebrafish using nonactivated eggs as recipients without the need to detect the micropyle was developed in our lab. However, the use of spermatozoa as an activating agent prevented to know whether the inserted nucleus compromised embryonic and early larval developmental ability. The aim of the present work was to test the developmental ability of the embryos reconstructed by transplanting adult fibroblast nuclei into the central region of the metaphase II egg but subsequently activated by only water. In addition, because an oocyte aging facilitates the activation in mammalian oocytes, this work also pursued to test whether the use of limited-aged eggs (2 h) as recipients improved the activation process in zebrafish NT. The adult somatic nucleus located in the central region of the nonactivated egg resulted in the 12% of mid-blastula transition embryos versus the 20% when the transplant is in the animal pole ( p ≥ 0.05). This suggests that the central region of the nonactivated metaphase II eggs can be a suitable place for nucleus deposition in NT in zebrafish. These results reinforce the possibility to use nonactivated metaphase II eggs in subsequent reprogramming studies by adult somatic NT in zebrafish. Unfortunately, in contrast to mammals, a limited egg aging (2 h) did not improve the activation process in zebrafish NT.