FIG. 4.

Transcription pattern of cis regulatory intergenic sequences in the bithorax complex. RNA in situ hybridization was performed with 1- to 12-h embryos. cis regulatory sequences are marked by red bars. Homeotic genes according to their most common splicing form are illustrated in black, and the in situ hybridization probes are marked in blue. The upper panels show embryos of the blastula stage, whereas the lower panels depict embryos around germ band extension. All the transcripts depicted are in distal-to-proximal orientation, detected by strand-specific probes. Transcripts remained through embryogenesis or appeared at later stages, as shown for probe D 1E1. The anterior expression domains of CMMs and intergenic cis regulatory sequences are transcribed in a linear pattern along the distal-proximal axis of the bithorax complex. Probe D 1E1 detects transcripts in the most posterior parasegment 14, although only after germ band retraction. Fab7 hybridized to transcripts in parasegments 12 to 14; Mcp to parasegments 10 to 14; iab4 to parasegments 8 to 14; and the bxd PRE to parasegments 6 to 12.