Fig. 4: Loss of BMP expression and abnormal epithelial proliferation in the Foxl1-deficient fetal small intestine.

A Model for partitioning of small intestinal epithelial cells into postmitotic villus cells and proliferating intervillus cells through BMP signals emanating from villus cluster cells. Modified after Shyer and colleagues². B Expression of multiple Bmp genes is reduced in telocyte progenitor 1 cells in the absence of Foxl1. UMAP and violin plots for telocyte progenitors 1 and 2 as well as smooth muscle cells or Mesenchymal progenitor-1 for comparison. Statistical significance was assessed using a two-sided Wilcoxon rank-sum test. Smooth muscle cells (Control vs Foxl1 null): Bmp2, *, p = 0.047; Bmp3, ns, p = 0.140; Bmp4, ns, p = 0.382; Bmp5, ns, p = 0.66; Bmp6, ns, p = 0.147. Telocyte prog-1 (Control vs Foxl1 null): Bmp2, ****, p < 2 × 10⁻¹⁶; Bmp3, ***, p = 9.2 × 10⁻⁴; Bmp4, ****, p < 2 × 10⁻¹⁶; Bmp5, ****, p < 2 × 10⁻¹⁶; Bmp6, **, p = 0.0017; Bmp7, ns, p = 0.65. Telocyte prog-2 (Control vs Foxl1 null): Bmp2, ns, p = 0.312; Bmp3, ns, p = 0.886; Bmp4, *, p = 0.024; Bmp5, ns, p = 0.52; Bmp6, ns, p = 0.703; Bmp7, ns, p = 0.17. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001. C Determination of BMP signaling pathway activation by immunofluorescence staining for phosphorylated Smad1/5 (p-Smad1/5), downstream mediators of BMP receptor activation, in the fetal gut (E15.5). Shown are both single optical sections as well as z-stack projections without the DAPI counterstain to better visualize the p-Smad1/5 signal. D Immunofluorescence staining of the 15.5 dpc anterior small intestine from control and Foxl1 null mice for the WNT target gene Sox9 (green), the proliferation marker Ki67 (red), and epithelial E-cadherin (white). Nuclei were counterstained with DAPI (blue). For imaging analyses (C, D), 3–5 embryos per genotype at the indicated developmental stages were examined, and representative images are shown.