Figure 3.

Expression of S6k during development and in Drosophila air8 cultured blood cells. (A) The 3.0-kb and 5.0-kb S6k transcripts are expressed at all stages of development and share a common open reading frame. A minimum of two smaller transcripts that differ in their 5′ ends from the major transcripts (data not shown) are found at all stages but in lower steady-state levels. (B) The smaller S6k transcripts are more abundant in total RNA derived from cultured Drosophila air8 blood cells [established from the neoplastic blood cells of RpS6^air8 mutant larvae (21)] when compared with adult female RNAs. Poly(A)⁺ RNA was isolated from wild-type animals at the following developmental stages: embryonic, 4–8 hr, 8–12 hr, 12–16 hr, and 16–20 hr; larval, including first-instar, second-instar, early third-instar, and late (wandering) third-instar; pupal, including mid-pupae (degraded) and late pupae; adult total RNA from mixed-aged females. The S6k probe used in all of the experiments included sequences derived from the catalytic domain, C-terminal domain, and the 3′ UTR. Variations in sample loading on the gels were assessed by probing the filters with RpS6 sequences, which were shown to express consistent levels of 0.9- to 1.1-kb mRNA transcripts throughout development (21).