(A-D) Longitudinal and (EL) cross-sections of muscle from 6-months old wild-type and Tln1HSA-CREko mice were stained with antibodies to costameric proteins and ECM glycoproteins and analyzed by immunofluorescence microscopy. The integrin β1-subunit, α-actinin, vinculin, dystrophin, collagen type IV and laminin were normally localized in the mutants. (M-P) Analysis of muscle by transmission electron microscopy. Sarcomere organization was not affected in Tln1HSA-CREko mice (M,N), but sarcomeres occasionally appeared hypercontracted (O,P). The Z-band was always detectable (O,P, arrows), but the A band (O,P, asterisk) was sometimes not evident in contracted muscle fibres. Scale bars: (A-L) 200 μm; (M,N), 2 μM; (O,P) 1 μm.