THE FATES OF THE BLASTOMERES OF THE 16-CELL ZEBRAFISH EMBRYO

We present a fate map for the 16-cell-stage blastomeres of the zebrafi sh embryo Brachydanio rerio. We injected high molecular weight fluores cent dextran into cleavage-stage cells to observe the contributions of the descendants of the first 16 cells to the adult. The patterns deri ved from these early cells are similar, but not identical among differ ent embryos. Furthermore, two-color injections showed that sister blas tomeres at the 16-cell stage regularly contribute to different sets of adult structures. A few of the scored tissues could not be mapped in a manner consistent with the predicted axes. Other tissues were mapped to several of the 16 blastomeres. Many of the tissues map with high p robability to a few 16-cell-stage blastomeres. Thus, based on 112 inje ctions in 56 different embryos, we have constructed a fate map by assi gning probabilities for the contribution of each blastomere to each of 31 tissues in the 26-hour embryo.