Fig. 4. The unfolded protein response (UPR) is triggered in wol embryos. (A) Splicing of xbp1 mRNA was examined by RT-PCR. In wild-type Drosophila embryos, only the unspliced 127 bp product was detected, whereas some spliced 104 bp xbp1 message was found in wol¹ embryos. In untreated S2 cells, mostly unspliced product is present. Tunicamycin (tm) or DTT treatment shifts the ratio of spliced/unspliced in favor of the spliced product. (B) Increased eIF2 phosphorylation in wol embryos. Western blot analysis of phosphorylated and total levels of eIF2. The ratio of phosphorylated/total eIF2 was calculated from two independent experiments.