Correlation between speed and turning naturally arises for sparsely sampled cell movements.

Area of Science:

• Cellular and Molecular Biology
• Biophysics
• Immunology

Background:

• Cell movement mechanisms are not fully understood.
• Cell persistence, defined by turning angles (TA), influences displacement.
• Previous studies suggest a cell-intrinsic program links lower TA (higher persistence) to faster cell speeds.

Purpose of the Study:

• To investigate the correlation between cell speed and turning angles (TA) in CD8 T cells.
• To determine if cell-intrinsic programs or other factors explain the observed negative correlation.
• To explore the impact of sampling frequency on inferred cell motility parameters.

Main Methods:

• Confirmed the speed-TA correlation in 3D movement data of CD8 T cells from murine lymph nodes and liver.
• Simulated correlated random walks using von Mises-Fisher (vMF) and Ornstein-Uhlenbeck (OU) processes.
• Analyzed the effect of trajectory sub-sampling (imaging frequency) on the speed-TA relationship.

Main Results:

• The negative correlation between TA and speed was confirmed in multiple datasets, including during blood flow.
• Simulations demonstrated that sub-sampling trajectories can naturally generate the speed-TA correlation.
• This effect is pronounced when sampling frequency matches the inverse of cell persistence time and when cell persistence varies.
• Lower imaging frequency led to slower estimated cell speeds, independent of intrinsic cell programs.

Conclusions:

• Sub-sampling of cell trajectories can significantly contribute to, or fully explain, the observed negative correlation between speed and turning angles.
• The frequency of imaging is a critical factor in accurately inferring cell motility parameters like speed and persistence.
• The findings challenge the sole reliance on cell-intrinsic programs to explain observed cell movement correlations.