Physical model of axonemal splitting

Area of Science:

• Biophysics
• Cell Biology
• Biomechanical Engineering

Background:

• Ciliary axonemes possess a complex 9+2 microtubule structure responsible for motility.
• Microtubule sliding, driven by dynein motor proteins, is fundamental to ciliary bending.
• Previous models explained microtubule sliding but not bending moment generation in anchored axonemes.

Purpose of the Study:

• To extend a physical model of microtubule sliding to investigate bending moment generation in anchored ciliary axonemes.
• To analyze how restricted sliding and dynein arm activity lead to the splitting of the microtubule array.
• To correlate observed splitting patterns with specific dynein arm activation and the switch-point hypothesis.

Main Methods:

• Developed and extended a physical model of microtubule sliding dynamics.
• Analyzed the shearing interactions between adjacent microtubule doublets.
• Investigated the role of interdoublet links and dynein arm activity in inducing array splitting.
• Correlated model predictions with electron microscopy of split axonemes.

Main Results:

• Restricted microtubule sliding generates bending moments due to polarized dynein arm activity.
• Bending moments cause the 9+2 microtubule array to split into multiple sets of doublets.
• Splitting patterns are determined by the location of active dynein arms and the integrity of interdoublet links.
• Model predicts specific dynein arm activation patterns consistent with the switch-point hypothesis of ciliary motion.

Conclusions:

• The physical model successfully explains bending moment generation and array splitting in anchored axonemes.
• Dynein arm activity and mechanical properties of interdoublet links are critical for ciliary motion and structural integrity.
• The findings support the switch-point hypothesis and provide insights into the mechanics of ciliary beating.