Fig. 4. schizo encodes two Arf-GEF-like proteins. (A) Schematic drawing of the schizo locus. Two transcripts are represented by EST clones identified by the BDGP (t1 RE44556, t2 LP01489). Transcription is from left to right. The location of two P-element insertions is indicated, both l(3)3 and P224 lead to a strong schizo mutant phenotype (data not shown). (B) The two deduced Schizo proteins are characterized by three sequence domains: an IQ domain, which might confer Calmodulin binding, a Sec7 and a Plecstrin homology (PH) domain, which are a signature of guanine exchange factors. (C) schizo is expressed maternally and appears to be negatively regulated by segmentation genes (D). (E,F) schizo is broadly expressed during early development. (G) At the extended germ band stage expression of schizo in the ectoderm is reduced. (H) schizo continues to be expressed in the central nervous system (CNS). The arrow denotes expression in the CNS midline.