Zygotic genes that mediate torso receptor tyrosine kinase functions in the Drosophila melanogaster embryo

The developmental signal that specifies the fates of cells at the anterior and posterior termini of the Drosophila embryo is transmitted by the torso receptor tyrosine kinase. This paper presents the results of a genetic interaction test for zygotic loci that act downstream of torso in the terminal genetic hierarchy. Tests of 26 zygotic mutants with defects in terminal development indicate that at least 14 reside in this hierarchy. The phenotypes associated with these genes fall into three classes, each of which represents a distinct aspect of terminal development and evolution. Four of the genes have been molecularly cloned and their products include an intercellular communication factor and three kinds of transcription factors.