Fig. 2

drl-positive LPM cells give rise to iSMC. (A) Schematic of the drl:creERT2×ubi:lox-EGFP-lox-mCherry (ubi:switch) crosses. Double-positive embryos were induced at the one-somite stage with 4-OH tamoxifen (10 µM final concentration). This activates the Cre recombinase, which then excises the loxP-flanked EGFP cassette and brings mCherry under control of the ubi promoter to lineage trace the switched cells. Photomicrographs of transverse vibratome sections of posterior trunk region (dr:creERT2;ubi:Switch) are shown below. Sections were imaged with a Zeiss LSM710 40× objective. Scale bar: 50 µm. Higher magnification of the intestinal region. The merged channel comprises EGFP, mCherry and DAPI. (B) Transverse vibratome sections of the posterior trunk region (dr:creERT2;ubi:Switch). Higher magnifications of the intestinal region. iSMCs are stained using transgelin antibody to compare with lineage labeling by drl:creERT2. Scale bar: 30 µm. The merged channel comprises EGFP, mCherry and DAPI. (C) Transverse vibratome sections of the posterior trunk region (drl:creERT2xubi:switch). Higher magnification of the intestinal region showing the different switching efficacy for iSMCs after 4-OH treatment at the one-somite stage. Class I, few iSMC are switched; class II, half iSMC are switched; class III, the entire population of iSMCs surrounding the gut are switched. The occurrences of the switching efficacies are: class I, 28% (9/31); class II, 50% (15/31); class III, 22% (7/31). Asterisks indicate switched iSMCs. Sections were imaged with a Zeiss LSM710 40× objective. Scale bar: 25 µm. The merged channel comprises EGFP, mCherry and DAPI.