Figure 3.

A genetic eyFLP/FRT-based screen in Drosophila identifies Madm as a positive growth regulator. (a-d) Dorsal view of mosaic heads generated by means of the eyFLP/FRT system. (a) The isogenized FRT82 chromosome used in the genetic screen produces a control mosaic head. (b, c) Heads largely homozygous mutant for an EMS-induced Madm mutation display a pinhead phenotype that can be reverted by one copy of a genomic Madm rescue construct (d). (e) Graphic representation of the Drosophila Madm protein (top) and gene (bottom). In the protein, the BunA-binding region and the NES and NLS sequences are indicated (netNES 1.1 [63], ELM [64], PredictNLS [65]). The seven alleles isolated in the genetic screen and the sites of their EMS-induced mutations are in red. Amino acid changes in the protein are indicated. In alleles 3Y2 and 7L2, the first nucleotide downstream of the first Madm exon is mutated, thus disrupting the splice donor site. In allele 2D2, a deletion causes a frameshift after amino acid 385, resulting in a premature translational stop after an additional 34 amino acids. Alleles 3Y2, 4S3, and 7L2 lead to a pinhead phenotype of intermediate strength (b) whereas 2D2, 2U3, and 3G5 produce a stronger pinhead phenotype (c). The hypomorphic allele 3T4 generates a weak pinhead phenotype (data not shown). Genotypes of the flies shown are: (a) y, w, eyFlp/y, w; FRT82B/FRT82B, w⁺, cl^3R3; (b, c) y, w, eyFlp/y, w; FRT82B, Madm^{7L2 or 3G5}/FRT82B, w⁺, cl^3R3; (d) y, w, eyFlp/y, w; gen.Madm(LCQ139)/+; FRT82B, Madm^3G5/FRT82B, w⁺, cl^3R3.