Analysis of cytoplasmic activity dependent on the Drosophila terminal pattern gene torso.

Cytoplasm from wildtype Drosophila embryos was transplanted into torso (tor) mutant embryos to determine the distribution of terminal rescuing activity at the cleavage stage. Although posterior and lateral wildtype cytoplasm contained rescuing activity that restored posterior terminal (telson) structures Klingler et al. (1988, Nature (London) 335, 275-277) this rescuing activity was not found in anterior cytoplasm. Similarly, transplantation of anterior and lateral wildtype cytoplasm into the anterior of tor embryos rescued anterior terminal (acron) structures, whereas posterior cytoplasm did not. This failure of reciprocal rescue is due to the presence of the products of the anterior and posterior classes of genes, because anterior cytoplasm from bicoid mutant embryos restored the telson in the posterior as well as the acron in the anterior of tor embryos, and because posterior cytoplasm from nanos embryos rescued the acron in the anterior as well as the telson in the posterior of tor embryos. Therefore terminal rescuing activity is evenly distributed throughout the cleavage stage embryo as anticipated from molecular studies.