Fig. 5: TM9SF3 regulates cytoskeletal dynamics in ppl cells in response to an extracellular pH.

a Immunofluorescence images showing phosphorylated myosin light chain (pMLC), filamentous actin (F-actin), and nuclei in Tg(gsc:EGFP-CAAX) at 8 hpf in WT and tm9sf3^−/− backgrounds. Quantitative analysis of pMLC (b) and F-actin (c) levels in ppl at 7 and 8 hpf, corresponding to (a). Mean fluorescence intensity per embryo is plotted, with WT at 7 hpf set as 1 (WT: n = 9 at 7 and 8 hpf; tm9sf3^−/−; n = 9 at 7 and 8 hpf). Data are presented as mean values ± SD. d Digital section images from (a), showing the distribution of pMLC and F-actin across ppl cells. The color spectrum indicates relative signal intensity. Regions corresponding to the front and rear of ppl are highlighted with yellow and blue boxes, respectively, and shown at higher magnification below. e Quantitative comparison of the pMLC to F-actin ratio from the front to the rear of ppl based on (d). f Live images of ppl cells at the leading edge of Tg(gsc:EGFP-CAAX) in WT and tm9sf3^−/− backgrounds expressing injected Lifeact-RFP mRNA at 7 hpf. White arrows indicate filopodia formation at the leading edge of ppl. WT and tm9sf3^−/− embryos correspond to those in Supplementary Fig. 6, (e) and Fig. 4, (f), respectively. Results are representative of two independent embryos. g Fluorescence images of mixed ppl cells from WT and tm9sf3^−/− embryos incubated in the medium adjusted to pH 7 or 8 for 1, 4, and 8 hours. Results are representative of two independent experiments. h Schematic model summarizing cytoskeletal dynamics in WT and tm9sf3^−/− ppl cells under low pH environment. All source data are provided as a Source Data file. Scale bars, 50 µm (a, d), 10 µm (enlarged panels in d), 20 µm (f, g).