POSITIONAL INFORMATION ALONG THE DORSAL-VENTRAL AXIS OF THE DROSOPHILA EYE - GRADED EXPRESSION OF THE 4-JOINTED GENE

Several observations suggest that developing ommatidia in the Drosophi la eye have distinct dorsal-ventral (d-v) positional identities, despi te their morphological uniformity. To identify molecular differences a long the d-v axis of the eye, we carried out a systematic screen for P -element insertions that show nonuniform reporter gene expression alon g this axis. We identified P-element insertions in which lacZ expressi on is activated in dorsal, ventral, or equatorial regions of the disc. These patterns of transcriptional enhancer activity are established e arly in disc development and are maintained in a size invariant manner during disc growth. Several insertions with an equatorial-to-polar gr adient of lacZ expression disrupt the four-jointed (fj) gene which is required for proper leg, wing, and eye development. The fj cDNA sequen ce includes a presumptive internal signal sequence, indicating that fj encodes a cell surface or secreted protein. Analysis of the fj phenot ype and expression pattern in the leg suggests that fj is required for cell-cell signaling during disc development. (C) 1996 Academic Press, Inc.