Fig. 4. PINCH is dependent on integrins for its enrichment at muscle-attachment sites. (A,B) Optical section through a stage 16 embryo, showing localization of the indicated proteins at the muscle-attachment sites. (A) PINCH immunoreactivity. (B) ßPS integrin immunoreactivity. The merge of the boxed regions in the stained embryos is shown in the lower corner of the panel. (C,D) Optical sections near the lateral surface of stage 16 embryos stained for PINCH. (C) PINCH enrichment at muscle-attachment sites in wild-type muscle cells. (D) PINCH distribution in myospheroid mutant muscle cells. Note lack of enrichment at the muscle termini (arrows). (E,F) Lateral views of stage 16 myospheroid embryos. (E) PINCH distribution. (F) Pak distribution. Pak remains prominently enriched at muscle-attachment sites (arrows in F), while PINCH is diffuse. Arrowheads in E indicate background immunoreactivity against chordotonal organs present in the affinity-purified PINCH antiserum. (G,H) Ventral views of stage 16 embryos stained with a monoclonal antibody against ßPS integrin. (G) ßPS integrin distribution in a wild-type embryo. (H) ßPS integrin distribution in a stck¹⁸/l(3)097 embryo. ßPS integrin remains enriched at the muscle-attachment sites, indicating that functional PINCH is not required for integrin localization to the myotendinous junction.

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