In bony fish, somatic-lineage blastomeres in the blastula are thought to possess pluripotency and differentiate into mesoendoderm lineages through induction from the yolk cells. This is supported by their ability to alter their developmental fate when transplanted from their original location to a different area around the blastoderm during the blastula stage. However, whether pluripotency can be sustained under dissociated conditions without cytokines remains unclear. Here, we conducted experiments to clarify the differentiation potential of blastomeres dissociated at the mid-blastula stage in goldfish (Carassius auratus). When dissociated blastomeres were cultured under conditions chelated with 0.25% trisodium citrate at 20˚C, they began to aggregate and formed cell clusters after 6 h, whereas control embryos developed to the germ-ring stage. When dissociated blastomeres were cultured for 12 h and then transplanted into host blastulae, most donor cells were incorporated as clusters into the host organs and differentiated exclusively into the ectoderm lineage. These results suggest that, in the absence of cytokines, blastomeres at the blastula stage are destined to differentiate into the ectoderm lineage.
Urushibata et al. (Mon,) studied this question.