1Laboratory of Aquaculture Genetics and Genomics, Division of Marine Life Science, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan, 2Nanae Fresh-Water Laboratory, Field Science Center for Northern Biosphere, Hokkaido University, Nanae, Kameda, Hokkaido, Japan
In teleosts, viable nucleocytoplasmic hybrids, formed by combining a nucleus from one species with the egg cytoplasm of another, have been used as one of the methods for breed improvement in aquaculture, but have been little exploited for developmental biology studies. Here, we used an artificial androgenesis technique to form nucleocytoplasmic hybrids comprising a goldfish haploid nucleus and loach egg cytoplasm. These hybrids were used to investigate interactions between the nucleus and cytoplasm during embryonic development. Additionally, the developmental characteristics of embryonic cells of nucleocytoplasmic hybrids were examined in chimeras produced by transplantation of blastomeres into recipient loach or goldfish embryos. We found that the nucleocytoplasmic hybrids arrested at the dome stage of embryonic development and did not form any gastrula structures. The goosecoid (gsc) and no tail (ntl) genes were expressed normally before gastrulation in nucleocytoplasmic hybrids, similar to diploid loach. However, expression of the gsc and ntl genes was not maintained in nucleocytoplasmic hybrids. In chimeric embryos, blastomeres derived from nucleocytoplasmic hybrids were found to mix with the cells of recipient loach embryos at the gastrula stage. The transplanted blastomeres formed small clusters at the somitogenesis stage and, finally, small spots at the hatching stage. In contrast, when the blastomeres were transplanted into goldfish embryos, the transplanted blastomeres aggregated in the chimeric embryos. Thus, embryonic cells from nucleocytoplasmic hybrids that arrest before gastrulation could survive beyond the somitogenesis stage depending on the cytoplasmic environment in the recipient embryos.