S1pr2/Gα13 signaling is required for convergent movement of the anterior endoderm during segmentation. (A-I) Epifluorescence images of the anterior endoderm in Tg(sox17:EGFP) control, milm93 mutant or gnb13ab MOs-injected embryos raised at 25°C at the indicated stages. Yellow lines (equivalent length among embryos at the same stage) indicate the width of the anterior endodermal sheet; red asterisks indicate endodermal holes. (J) Quantification of endoderm width in each group. *P<0.05, **P<0.01 versus control. Data are mean±s.e.m. (K) The cell-transplantation procedure. Sox32-overexpressing and rhodamine-dextran labeled wild-type or s1pr2 morphant donor cells were transplanted into Tg(sox17:EGFP) host embryos. (L-O) Still images from time-lapse movies, showing the anterior endoderm in wild-type Tg(sox17:EGFP) hosts transplanted with rhodamine-labeled donor cells (L,M are wild type; N,O are s1pr2 morphant) at 3 and 10 somites. Green and red lines indicate the width of the host and donor endodermal sheets, respectively. (P) Convergence velocity of the wild-type and s1pr2 morphant endoderm populations. **P<0.001; #P=0.96 versus the control. Data are mean±s.e.m. Scale bars: 100 μm.
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