Packing of actin filaments in single and double mutants. Stereocilia were prepared for transmission EM using dehydration. (left) Stereocilia cross sections from indicated genotypes; all panels are 300 nm wide. (middle) Cropped FFT transforms of spatial images. (right) Distribution of cross-linker distance determined by FFT analysis and fit with a single Gaussian function. (A) Wild type (C57BL/6). The ring in the FFT image indicates liquid packing. (B) Pls1^−/−. These stereocilia had six peaks of equal intensity in FFT, which indicates hexagonal packing. (C) Fscn2^R109H/R109H. The FFTs from these stereocilia displayed a ring with some hexagonal definition. (D) Pls1^−/− Fscn2^R109H/R109H double mutants. These stereocilia had six peaks in the FFT like in Pls1^−/−, but often two opposing peaks were more intense than the four flanking peaks.