Fig. 5.

The distal C terminus of β_1a is crucial for DHPR tetrad formation. (A and B) Representative freeze-fracture replicas from tail muscle tissue of 27- to 30-hpf relaxed zebrafish expressing β₄/β_1a(C) (A) or β₄/β_1a(dist.C) (B) reveal accurate arrangement of DHPR particles in tetrads. The red dots (Bottom) indicate the centers of three- or four-particle tetrads and additional particles that are in the expected position for an orthogonal array. (Scale bar, 50 nm.) (C) Numbers of tetrads (three or four particles) determined by two independent investigators from 95 anonymized freeze-fracture images acquired from zebrafish tails, either normal controls (normal), uninjected (relaxed), or injected with β₄, β₄/β_1a(C), or β₄/β_1a(dist.C) mRNA. Each bar represents mean of the counts normalized to normal zebrafish (where the mean of the two investigators’ counts was defined as 100%) and the two arrows (red and green) depict the counts of the two individual investigators (SI Appendix, Table S2). (D) Counts of DHPR particles per junction from zebrafish tails, either uninjected (relaxed), injected with β₄, β₄/β_1a(C), or β₄/β_1a(dist.C) mRNA, or normal controls (normal). Error bars indicate SEM. P determined by unpaired Student’s t test, *P < 0.05; **P < 0.01.