Cover image

Cover Establishment of segment-polarity gene expression patterns in Drosophila is controlled at the level of transcriptional elongation. Shown here is the ventral view of a gastrula-stage Drosophila embryo showing the mRNA expression pattern of the segmentation gene, sloppy-paired-1 (slp1; green), and a reporter gene that expresses lacZ mRNA (red) under control of a slp1 cis-regulatory element. The segmentally repeated expression of slp1 at this stage is in response to regulatory input from transcription factors encoded by the pair-rule segmentation genes. (For details, see Wang et al., p. 1031.) Image courtesy of Lisa Prazak, Janet Chang, Miki Fujioka, James Jaynes, and J. Peter Gergen.