lbe transcript appears earlier, and is more abundant, than the lbl transcript. Both transcripts are expressed in the anal plate primordium, with lbl expression starting at stage 10-11. At stage 10-11, expression is also detected in a cluster of cells corresponding to the heart primordium. During embryonic stages 10-13, lbe and lbl are both expressed in the dorsal ectoderm of abdominal segments 1-7, and to a lesser extent, in the ventral ectoderm. At stage 15, lbl and lbe transcripts persist in the dorsal, but not in the ven ral, epidermis. Later in embryogenesis, lbl and lbe transcripts are restricted to clusters of cells in the central and peripheral nervous systems, and to the segment border muscles.

Using RT-PCR, lbl transcript is detected in embryogenesis 2 hours after lbe, and persists through embryogenesis. lbl transcript is detected in stage 13 embryos, in the dorsal and ventral epidermis in a segmentally repeated pattern.

Using RT-PCR, lbl transcript is detected in 8-20 hr embryos, in third instar larvae, and in pupae. In-situ hybridization to stage 13-17 embryos reveals that lbl is expressed in parts of the developing central nervous system, including cells of the ventral nerve cord. Strongest expression is seen during early ventral cord condensation.