Fig. 8. rib mRNA is expressed throughout embryonic development. Whole-mount in situ hybridization to wild-type embryos with an antisense rib RNA probe. Images with primed letters are ventral views of the same embryo; all others are lateral views. Embryonic stages are indicated in the lower left corner. rib expression is first detected in the termini (A,B), but is absent from pole cells (arrowhead in A). Segmental stripes appear in the epidermis (arrowheads in B,C,C',E). Expression of rib RNA in the salivary gland primordia is evident by stage 10 (arrow in D), and is expressed throughout invagination (arrows in E,E',F'). The Malpighian tubules also express rib (arrowhead in G). By later stages, rib RNA is detected in most cells of the epidermis, including cells of the lateral epidermis. Of note is the lack of elevated expression in the later central nervous system and midgut, two tissues whose formation is abnormal in rib mutants (Jack and Myette, 1997), perhaps indicating that these defects are indirect. Alternatively, earlier expression or a lower level of rib is required in these tissues.
