Fig. 2. Activated Pelle kinases generate multiple dorsoventral patterning thresholds. Mutant embryos at the cellular blastoderm stage were collected from females homozygous for a null mutation in gd. The embryos lack an endogenous dorsoventral Dorsal nuclear gradient. The embryos in C-E contain the Pelle-Tor⁴⁰²¹ transgene, while the embryos in F-H contain a Pelle-Tor fusion gene. Both transgenes were expressed at the anterior pole of mutant embryos using the bcd 3' UTR. Embryos were stained with snail (C,F), vnd (D,G), and sog (E,H) hybridization probes. (A) Total protein extracts from wild-type and transgenic embryos were fractionated on a polyacrylamide gel, transferred to a membrane, and then incubated with an anti-Pelle antiserum. Lane 1 contains an extract from wild-type embryos (yw). The Pelle kinase has an apparent molecular weight of 75kDa. Lanes 2 and 3 contain extracts from transgenic embryos carrying either the Pelle-Tor⁴⁰²¹ (lane 2) or the Pelle-Tor (lane 3) fusion protein. Both full-length proteins have an apparent molecular weight of 140kDa (the band at 95kDa is a putative degradation product). There are slightly higher levels of Pelle-Tor (lane 3) than Pelle-Tor⁴⁰²¹ (lane 2). (B) The diagram depicts a precellular embryo that contains either the Pelle-Tor⁴⁰²¹ or the Pelle-Tor transgene. Pelle-Tor⁴⁰²¹ leads to the activation of snail at the anterior pole, whereas even high levels of the Pelle-Tor transgene fail to induce snail expression. (C) snail expression in mutant embryos that contain the Pelle-Tor⁴⁰²¹ transgene. Staining is restricted to anterior regions containing peak levels of the transgene. (D) vnd expression pattern. Staining is detected in a stripe just posterior to the snail expression pattern. (E) sog expression pattern. Staining is detected in a broad band in the anterior third of the embryo. Both vnd and sog are repressed at the anterior pole, probably by Snail.(F) snail is not expressed in mutant embryos that contain the Pelle-Tor transgene. (G) vnd is activated only at the very anterior tip of embryos that express the Pelle-Tor transgene. (H) sog exhibits a broader pattern of expression in these embryos.