PMC

ARepresentative SEM images (side view) of microvilli in the duodenum of CDHR5^+/+ and CDHR5^∆/∆ mice. Scale bar = 1 μm.BRepresentative TEM images showing longitudinal sections through microvilli. Scale bar = 500 nm.CBox plots with quantitative values of microvillus length.DRepresentative SEM images (top view) showing the brush border in the duodenum (insets represent Fast Fourier Transformation FFT frequency domain images of a representative image section). Scale bar = 1 μm.EHigh‐magnification SEM images (top view) of the duodenal brush border (left) and corresponding graphs with black spots (right) representing positions of microvillus tips in SEM images.F–HGraphs with black spots (as shown in E) were used for quantitation of microvillus numbers (F), nearest neighbor distances of microvilli (G) and frequency distributions of the nearest neighbor distances (H). HPF, high‐power field.ITEM images showing microvillus cross‐sections. The arrowhead indicates fused microvilli. Scale bar = 200 nm.J–LImages of microvillus cross‐sections (as shown in I) were used for quantitation of microvillus areas (J), frequency distributions of the microvillus areas (K) and calculation of microvillus circularity (L).MTEM images showing longitudinal sections through microvilli of CDHR5^+/+ and CDHR5^∆/∆ colonocytes. Scale bar = 500 nm.NBox plots with quantitative values of microvillus length.OSEM images (top view) showing the brush border in the colon (insets represent Fast Fourier Transformation FFT frequency domain images of a representative image section). Scale bar = 1 μm.PHigh‐magnification SEM images (top view) of the colonic brush border (left) and corresponding graphs with black spots (right) representing positions of microvillus tips in SEM images.Q–SGraphs with black spots (as shown in P) were used for quantitation of colonic microvillus numbers (Q), nearest neighbor distances of microvilli (R) and frequency distributions of the nearest neighbor distances (S). HPF, high‐power field.T–VTEM images of colonic microvillus cross‐sections were used for quantitation of microvillus areas (T), frequency distributions of the microvillus areas (U) and for calculation of microvillus circularity (V).
Data information: For (C) three mice per genotype and 45 microvilli per mouse were analyzed. For (F) five mice per genotype and one representative SEM image per mouse were analyzed. For (G and H) SEM images of three mice per genotype with > 340 microvilli per image were analyzed. For (J–L) TEM images of three mice per genotype with > 80 microvilli per image were analyzed. For (N) five mice per genotype and 50 microvilli per mouse were analyzed. For (Q) three mice per genotype and two representative SEM images per mouse were analyzed. For (R and S) SEM images of three mice per genotype with > 320 microvilli per image were analyzed. For (T–V) TEM images of three mice per genotype with > 80 microvilli per image were analyzed. Statistical analysis of all box plots was performed using unpaired Student's t‐test. *P < 0.05, **P < 0.01, ***P < 0.001 or ****P < 0.0001.
Source data are available online for this figure.

Conceptual model non-deformable (left, A-B) and deformable (right, C-D) microvilli in the cell-substrate contact area. For simplicity only one ligand per microvillus tip is shown. L₀, ΔL, F, and F₀ are the microvillus equilibrium length, extension, bond force, and threshold bond force, respectively. ΔL_te is the tether extension. (A-B) The microvillus length is assumed to be fixed, but the microvillus can pivot about its base. At time t microvillus M₁ has a load-bearing bond, microvillus M₂ has a bond bearing no load, and microvillus M₃ has no bond. At time t + Δt the bond of M₁ is already broken, the bond of M₂ is load-bearing, and the newly formed bond of M₃ has no load yet. (C-D) Microvilli are allowed to extend and form tethers. If F < F₀ at time t, then microvillus M₁ will be longer than in A. If F > F₀ at time t + Δt, then most likely the bond of microvillus M₁ will still exist (compare D with B), the microvillus will be longer than in C, and a tether will be developed.

Illustration for calculations of microvillus extension (A) and microvillus tether extension (B), for time step Δt. ΔL_old [(ΔL_te)_old] is the microvillus [tether] extension at the beginning of the time step, and ΔL_new [(ΔL_te)_new] is the microvillus [tether] extension at the end of the time step. ΔL(t) = (F/σ){1−exp[−t/(η/σ)]} and ΔL_te(t) = [(F–F₀)/η_te] t, where F, F₀, σ, and η are the microvillus bond force (assumed to be constant for the time step), threshold force, spring constant and effective viscosity, respectively. Symbol η_te denotes the effective viscosity of the microvillus tether.

(A) Deformation history for the microvillus marked with one asterisk in . The lifetimes of three load-bearing bonds, B1, B2, and B3, developed by the microvillus, are represented by the green horizontal bars. F₀ is the microvillus’s threshold force. (B) Similarly, the deformation history for the microvillus marked with two asterisks in . The arrows point to episodes in microvillus extension which are too short to be visible in the diagram as black segments. (C) Bond force acting on the microvillus discussed in B. The dashed, horizontal line marks the microvillus threshold force.