Lineage Tracing of FOXL1+ Cells in the Tunica Muscularis Suggests Mutual Origin for Telocytes and Smooth Muscle Cells.

We recently identified a FOXL1+ intestinal subepithelial network of telocytes (TCs) without which epithelial stem and progenitor cells cannot proliferate and support regeneration. In addition to FOXL1 lineage cell distribution along the intestinal epithelium, we also observed their presence within the muscle layers. Here, we characterized FOXL1+ lineage cells along the muscle layers of the duodenum in order to understand their progeny and relation to interstitial Cajal cells (ICCs), smooth muscle cells (SMCs) and the previously reported PDGFRa+ TCs. Using a FOXL1-Cre transgenic line in conjunction with genetic lineage labeling using the Rosa26-mTmG allele, in which Cre-marked cells produce a membrane-targeted version of green fluorescent protein (GFP), we found that within the muscle layers FOXL1 lineage GFP+ cells had two main progeny; (i) elongated multinucleated SMA+ SMCs, intermingled in parallel or perpendicular to muscle fibers. (ii) TCs displaying small cell body with multiple cell processes, expressing PDGFRa and CD34. These findings may suggest a mutual origin for TCs and SMCs.