What they found
Pioneering electron microscopy and optical diffraction study of actin filament organization in stereocilia of alligator lizard cochlea. Established that stereocilia contain paracrystalline arrays of actin filaments with the long-axis crossover points in near-perfect register. The primary source for inter-filament spacing in mature cochlear stereocilia.
Numbers that matter
Inter-filament spacing:
- Generally cited as “~10 nm” inter-filament distance in stereocilia from this paper
- Filaments packed in scalloped rows (“festooned profile” in transverse section) — NOT simple hexagonal packing; instead a liquid-to-hexagonal hybrid
- Later work refines: Krey 2016 (Pls1 paper) measures 7.9–9.7 nm center-to-center by FFT analysis of freeze-substituted EM; espins give ~12 nm spacing, fascin ~6–8 nm
- Model’s STEREOCILIA_INTER_FILAMENT_NM = 12.0 corresponds to espin-crosslinked arrays specifically; native OHC core (plastin-1 + fimbrin) is ~9–10 nm
What the spacing tells us about bundling geometry:
- Filament center-to-center ~9–12 nm → outer surface distance ~2–5 nm (actin diameter ~7 nm)
- For a cross-linker to span two filaments it needs to bridge ~2–5 nm — this is geometrically plausible for a peptide (~3–5 nm extended)
- WH2 motif (~17–32 aa) = ~6–12 nm extended chain; could geometrically span two filaments IF it binds both with sufficient affinity (the key unproven assumption)
Source quality note:
- Full text behind Rockefeller University Press paywall (not PMC open access)
- Spacing value ~10 nm consistently cited across review literature as “Tilney et al. 1980”
- Krey 2016 (PMC5119939) is the modern measurement with EM + FFT, cites Tilney as historical reference; use Krey 2016 as primary quantitative source for spacing
Connections
- Stereocilia Actin Architecture — first measurement of inter-filament spacing in cochlear hair cells
- Krey 2016 Plastin Stereocilia Spacing — modern FFT-EM measurement; Tilney 1980 = ~10 nm historical, Krey 2016 = 7.9–9.7 nm
- Hydrogel Phase 4d F-actin Bundling Model — STEREOCILIA_INTER_FILAMENT_NM parameter should use 9–10 nm for OHC native, 12 nm if espin-dominated