Axonemal regulation by curvature explains sperm flagellar waveform modulation

Area of Science:

• Biophysics
• Reproductive Biology
• Computational Biology

Background:

• Flagellar motility is essential for natural and assisted reproduction.
• Sperm exhibit diverse motility patterns (progressive, activated, hyperactivated) crucial for fertilization.
• A unified mechanistic model for flagellar beat generation and modulation is lacking.

Purpose of the Study:

• To present a parsimonious mechanistic model for flagellar beat generation.
• To explain the modulation of sperm motility patterns.
• To provide a framework for quantitative analysis of flagellar dynamics.

Main Methods:

• Developed the Axonemal Regulation of Curvature, Hysteretic (ARCH) model.
• Integrated a curvature control theory with a nonlinear elastic flagellar model and viscous fluid dynamics.
• Utilized computational simulations to explore parameter effects and analyze flagellar limit cycles.

Main Results:

• The model generates beat patterns qualitatively matching penetrative, activated, and hyperactivated sperm motility modes.
• Identified a cusp catastrophe between progressive and nonprogressive motility.
• Observed hysteresis in motility response to critical curvature changes.
• Model shows good quantitative agreement with experimental human sperm curvature data.

Conclusions:

• The ARCH model offers a mechanistic explanation for flagellar motility modulation.
• The model accurately reproduces diverse sperm swimming behaviors.
• Provides a quantitative framework for interpreting sperm motility imaging data in reproductive contexts.