Generation of a null allele for smash. (A) Genomic structure of the smash locus. The exon-intron structures of the two smash transcripts smash-RM, encoding the Smash PM isoform, and smash-RI, encoding the Smash PI isoform, are indicated. Noncoding exons are gray, and coding exons are red. Exons of adjacent transcription units are shown in gray (noncoding) and blue (coding), respectively. The position of transposons used for the generation of defined deletions are indicated above the genomic map. The extent of the deletions in the smash³⁵ (middle) and smash^4.1 (bottom) alleles is indicated by boxes. (B and C) An embryo heterozygous for smash³⁵ and the balancer chromosome TM3[twi::GFP] stained for DAPI, GFP (B), Smash, and Baz (C) shows expression of GFP in the mesoderm and Smash localized at the ZA in the epidermis. (D and E) A smash³⁵ homozygous mutant embryo stained as in B and C lacks staining for GFP and Smash. C and E are higher-magnification views of the epidermis of the embryos shown in B and D, respectively. Anterior is to the left and dorsal is up. Bars: (B and D) 100 µm; (C and E) 10 µm.