Fig. 1. Kette has a mesoderm intrinsic essential function for myoblast fusion. kette mutants show a strong defect in muscle fusion that is due to an intrinsic mesodermal function of Kette. (A-F) Anti-ß3-Tubulin fluorescent staining of stage 16 embryos shows the myogenic defects of kette mutants. (A) Wild-type muscle pattern; (B) kette^J4-48 (null allele), which shows many unfused myoblasts, even at stage 16. (C) Hypomorphic allele kette^G1-37. (D-F) Detailed magnifications of A-C. The dorsal vessel (dv) is formed correctly in all kette mutants. (E) kette^J4-48 null mutant: mini-muscles are indicated by arrows. (F) kette^G1-37 stage 16 embryo: the unfused myoblasts have vanished. Large gaps in the muscle pattern and attachment defects (arrow) are visible. (G,H) Anti-Kette antibody staining on wild-type embryos shows the mesodermal expression of Kette. (G) In stage 16 embryos, the protein concentrates towards the muscle tips. (H) In stage 14 embryos, when muscle fusion takes place, Kette can be found in the whole somatic mesoderm. (I,J) Overexpression of Kette in the mesoderm in a kette mutant background with the help of a twi-GAL4 driver line rescues the kette phenotype. (I) Ventrolateral view of a rescued stage 16 embryo. (J) Higher magnification and lateral view of a rescued stage 16 embryo; only a few unfused myoblasts can be detected (arrow). (K) Anti-Kette (green) anti-ß-galactosidase (red) double labelling of rP298-expressing stage 13 wild-type embryo. (L,M) Anti-ß3-Tubulin and anti-Alien double labelling, monitoring the muscle attachment to the epidermis. (L) Wild-type stage 16 embryo with properly attached muscles. (M) Stage 16 kette^G1-37 mutant showing partly attached (arrowhead) and partly unattached (arrows) muscles. Unless otherwise stated, embryos in all figures are orientated with anterior towards the left.