Fig. 7. Functional mapping of domains important for hbs function. Wild type (A,E,I,M) or twist-GAL4; Dmef2-GAL4-driven overexpression of UAS-hbs^FL (B,F,J,N), UAS-hbs^ECD (C,G,K,O) and UAS-hbs^ICD (D,H,L,P) in embryos stained for Myosin (A-H), Krüppel (I-L) and Fasciclin III (M-P). All panels are lateral views of stage 16 (A-H), stage 14 (I-L) and stage 12 (M-P) embryos. Overexpression of UAS-hbs^FL or UAS-hbs^ECD constructs throughout the mesoderm resulted in partial fusion block (arrowheads, E-G) and muscle losses (white asterisk, B; note also losses in C). Bent arrow in B indicates dorsal muscles that are abnormally fused together. Specification of the founder cell marker Krüppel was normal initially yet later showed an abnormal pattern (I-K). Bent arrows in J,K designate LT and DA1/DO1 muscle precursors showing an abnormal morphology, respectively. By contrast, UAS-hbs^ICD overexpression in forming somatic muscles did not appreciably interfere with myogenesis (D,H,L). Overexpression of either UAS-hbs^FL, UAS-hbs^ECD or UAS-hbs^ICD constructs in the visceral mesoderm resulted in defects in Fasciclin III expression (arrowheads), suggesting abnormal segregation of visceral mesoderm precursors (M-P). (Q) Schematic representation of the constructs used in this study. UAS-hbs^FL is a full-length hbs protein, UAS-hbs^ICD is a 1093 amino acid long version that lacks the cytoplasmic region, and UAS-hbs^ECD is a 277 amino acid long construct deleting the extracellular domain of the protein. Light gray boxes represent Ig-C2 domains, dark gray boxes represent Fibronectin type III domains and black boxes represent the transmembrane region.

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