Embryonic pattern in Drosophila is organized by a hierarchy of maternal and zygotic segmentation genes that interact to define increasingly precise spatial domains (reviewed by Scott & O’Farrell, 1986; Akam, 1987). A metameric body plan is already established by the onset of gastrulation (3 h postfertilization) such that each segment expresses the segment-polarity genes engrailed (en) and wingless (wg) in single-cell-wide stripes (Kornberg, Sidon, O’Farrell & Simon, 1985; Fjose, McGinnis & Gehring, 1985; DiNardo, Kuner, Theis & O’Farrell, 1985; Baker, 1987). The current challenge is to define specific segmentation gene interactions, to determine how they achieve this spatial refinement and how their spatial relationships give rise to the structural complexities of the mature larva.
The pattern of en expression defines two metameric registers: the en domain lies at the posterior of each segment and at the anterior of each parasegment (Martinez-Arias &...
