Section: New Results

Analysis of lateral organization of ordered domains at the plasma membrane surface

Participant : Charles Kervrann.

Paper under review.

In this study, we have analysed a recently designed probe, di-4-ANEPPDHQ, that can change its fluorescent properties depending on whether it is residing in two distinct phases (ordered phase vs disordered phase) of the tobacco cell plasma membranes. We performed a spatial analysis of small (<200 nm) ordered domains observed in multispectral confocal microscopy. We focused on relevant binary images, assumed to be realizations of a MRF-Ising model, depicting the spatial organization of ordered domains. The Ising model depends on 2 parameters: the external field parameter $h$ which controls the total fraction of the “ordered” phase and the interaction parameter which controls the spatial coupling. Maximum pseudo-likelihood methods were investigated to estimate parameters able to describe the spatial properties of ordered domains at the scale of 200 nm $\times$ 200 nm. Almost all estimates of the coupling parameter were positive excluding complete spatial randomness of ordered domains and showing a tendency to spatial aggregation at small distance. We then measured the strength of spatial aggregation through the calculation of the variability fraction explained by the spatial coupling. The mean fraction is low (0.5%) suggesting positive and limited interacting forces between neighbor ordered pixels. Altogether our simulations and analyses provided a probabilistic spatial characterization of PM ordered domains, indicating that recorded images showed a two-scale organization with spatial randomness at large scales (several micrometers) associated with spatial aggregation due to short-range interactions (up to 400 nm).

Partners: P. Gerbeau-Pissot, F. Simon-Plas (UMR 1088 PME INRA, Dijon) and K. Kiêu (MIA Unit INRA, Jouy-en-Josas)