Fig. 6.

Mutual dependence among desmin, keratin 18 (Krt18), and Krt19 for incorporation into the intermediate filament reticulum. A–C: flexor digitorum brevis (FDB) muscles from wild-type (WT), Krt18-knockout (KO), Krt18-dominant-negative (DN), Krt19-KO, and Des-KO mice, as well as mice lacking both desmin and Krt19 [double knockout (DKO)], were electroporated to overexpress FLAG-tagged versions of Krt18, Krt19, or desmin. After freezing and cross-sectioning, samples were labeled with anti-FLAG (green) and anti-desmin (red). The distribution of the FLAG label in individual fibers was scored as reticular (1:A), punctate (2:B), or disrupted (3:C). Images obtained with FLAG-tagged Krt18. Scale bars in A-C, 5 µm. D–F: quantitation of the scoring determined above. n = 2–3 muscles each from male and female mice of each genotype per condition. The results show that desmin assembles into a reticulum independently of the keratins, whereas Krt19 requires desmin and Krt18 requires both Krt19 and desmin for assembly into a reticulum (see Table 2 for statistical analysis).