A fate map for the 32-cell stage of Rana pipiens

A fate map of the progeny derived from all blastomeres of the 32-cell stage embryo of the leopard frog Rana pipiens has been generated. Embryos presenting regular cleavages were injected into two pairs of blastomeres with fluorescein- and Texas red-lysine dextran. By stage 21, embryos were sectioned and the tissue distribution of labeled clones was determined. The results of 93 clones were pooled to give a fate map which represents the derivation of each tissue from the different blastomeres of the 32-cell embryo. The results show that all blastomeres give rise to multiple tissues and all tissues are derived from at least two, and usually more, pairs of blastomeres. Although there is a general tendency for ectoderm to derive from the animal hemisphere, endoderm from the vegetal hemisphere, and mesoderm from the equatorial region, the boundaries between germ layers are not sharply defined at the 32-cell stage but rather appear as a series of overlapping zones. The fate map of R. pipiens is quite similar to that of Xenopus laevis but differs in some details that are discussed. As in all vertebrates, the R. pipiens fate map is not fully deterministic but nevertheless has predictive value in that tissues are populated by the progeny of the same blastomeres in different embryos.