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Fig. 2
TPM2 variants disrupt muscle development in Drosophila. (A) Transgenic expression assays used to characterize the effects of TPM2 variants on myogenesis. (B and C) TPM2 variants caused multiple phenotypes in slou-expressing muscles. (B) Diagram showing the 30 body wall muscles in an embryonic hemisegment; slou.Gal4-expressing muscles are shown in blue (modeled after ref. 7). Confocal micrographs of stage 16 embryos that expressed GFP-tagged Drosophila Tropomyosin 2 (Tm2), wild-type human TPM2, or pathogenic TPM2 variants (green), colabeled with myosin heavy chain (MHC, violet). Two hemisegments are shown for each embryo. Variant-expressing LO1 muscles showed multiple phenotypes, including rounded muscles (elongation), muscles attached to an incorrect tendon (wrong tendon, white arrows), muscles attached to 3 tendons (multiple tendons, white arrowheads), muscles absent from a segment (missing), and muscles with bent or hook-shaped morphology (misshapen; yellow arrows). (C) Histogram of variant phenotypes. (D and E) TPM2 variants reduced muscle length in nau-expressing muscles. (D) The nau.Gal4-expressing muscles are diagramed in blue. Confocal micrographs of stage 16 embryos that expressed GFP-tagged transgenes, labeled for GFP. Variant-expressing VO5 muscles were short or rounded, but other parameters of muscle morphology were largely normal. E122K expressing muscles showed the strongest phenotype (white arrows). GFP expression in VO4 muscles was highly variable. (E) Box plot showing VO5 length normalized to Tm2-expressing control. Significance versus Tm2-expressing muscles was determined by Fisher’s exact test (C) or 1-way ANOVA (E). Error bars, standard error of the mean (SEM). *(P < 0.05), **(P < 0.01), ***(P < 0.001), ****(P < 0.0001). n ≥ 66 muscles per variant; minimum 9 embryos per variant. Scale bars, 20 μm.