A blastoderm fate map of compartments and segments of the Drosophila head

The epidermis of the adult head of Drosophila is composed of the derivatives of three pairs of imaginal discs: the labial discs which form the proboscis, the cibarial discs which form the clypeolabrum, and the eye-antennal discs which form all of the remaining head structures (i.e., the eyes, antennae, head capsule, and maxillary palps). Both the proboscis and the eye-antenna are known to be subdivided into anterior and posterior compartments. This paper reports a gynandromorph fate map of the blastoderm primordia forming the compartments and segments of the adult head. The major results are: (1) For both the proboscis and eye-antenna, blastoderm cells giving rise to the anterior compartment are positioned anterior to cells giving rise to the posterior compartment. This result suggests that the relative anteroposterior position of blastoderm cells constitutes the positional basis for the segregation of anterior and posterior polyclones in different segments. (2) The clypeolabral primordium is adjacent and anterior to the eye-antennal primordium; the proboscis primordium is adjacent and anterior to the prothoracic primordium. Assuming that all segment primordia are of equal length in the blastoderm, the proboscis and eye-antennal primordia are separated by a gap in which three other segment primordia might fit. These results suggest that at the blastoderm stage, the Drosophila head consists of a series of six segment primordia of similar size.