Fig. 4. Pipe and Windbeutel are required for Alcian Blue staining of embryonic salivary glands. (A) A stage 16 wild-type embryo stained with Alcian Blue. (B) The same embryo at higher magnification. Staging is according to Campos-Ortega and Hartenstein (Campos-Ortega and Hartenstein, 1985). Embryos heterozygous (C) and homozygous (D) for pipe^C14 were stained with Alcian Blue, as were embryos heterozygous (E) and homozygous (F) for pipe³. Embryos homozygous for the RNA null allele pipe^C14 or for the protein null allele pipe³ failed to stain with Alcian Blue. By contrast, embryos homozygous for pipe², which affects only the Pipe-ST2 isoform, stain with Alcian Blue (G). Embryos homozygous for wind^T6 (H), wind^M88 (I) or wind^RP (J) do not produce Alcian Blue-staining material in their salivary glands.