Figure 1.
Serpent down-regulation is not sufficient for midgut MET. (a–d) Wild-type embryos before EMT (stage 9; a), during migration (stage 11; b), and after MET (stage 15; c and d). (a and b) Serpent is expressed in midgut cells before EMT (red; a) and starts being down-regulated after EMT, as the cells initiate migration (red; b). (c and d) By stage 15, midgut cells have formed a monolayer of columnar-shaped cells, with Baz (d1) and E-Cad (d2) localized to the apical side of the cells and βPS strongly localized to both the basal and apical domains (d3). (e) Plots of the average fluorescence intensity (represented as mean gray value) of Baz, E-Cad, and βPS in stage 15 midgut cells measured along the apical (A) to basal (B) axis of a cell (represented in d by red line). For every such plot of average fluorescence shown in this paper, each dotted black line represents the average of a minimum of 10 cells per embryo. The solid red line represents overall the average of six embryos. See Materials and methods for how quantifications were performed. Sharp peaks of Baz and E-Cad are seen at the apical side of the cell, with peaks for βPS integrins seen both apically and basally, with the basal peak of βPS slightly higher than the apical peak. (f–i)sna,twi mutants before EMT (stage 9; f), during migration (stage 11; g), and at stage 15 (h and i). In sna,twi double mutant embryos, Srp is expressed before EMT (f) and down-regulated by the start of germband retraction (stage 11; g), as in wild-type (a and b). (h) Stage 15 midgut cells in sna, twi mutants are rounded and multilayered. (i) Baz (i1), E-Cad (i2), and βPS (i3) do not localize as in wild-type (compare sna,twi, h and i, with wild-type, c and d). (j) Plots of the average fluorescence intensity across sna,twi mutant midgut cells show that peaks of Baz, E-Cad are lost. While the basal peak of βPS is completely absent, the apical peak of βPS is still there. n = 6 embryos per condition (minimum 10 cells per embryo). The posterior midgut in (a, b, f, and g) is demarcated by dashed yellow lines, and Hindsight (Hnt, green) labels midgut cells. White dashed lines in a and h indicate the apical side of the midgut, and yellow lines, the basal. Red boxes in c and h depict the area of the midgut epithelium shown in d and i. Confocal images are oriented with the anterior to the left and posterior to the right. Scale bars, 10 µm (c, d, h, and i) and 50 µm (a, b, f, and g).

Serpent down-regulation is not sufficient for midgut MET. (a–d) Wild-type embryos before EMT (stage 9; a), during migration (stage 11; b), and after MET (stage 15; c and d). (a and b) Serpent is expressed in midgut cells before EMT (red; a) and starts being down-regulated after EMT, as the cells initiate migration (red; b). (c and d) By stage 15, midgut cells have formed a monolayer of columnar-shaped cells, with Baz (d1) and E-Cad (d2) localized to the apical side of the cells and βPS strongly localized to both the basal and apical domains (d3). (e) Plots of the average fluorescence intensity (represented as mean gray value) of Baz, E-Cad, and βPS in stage 15 midgut cells measured along the apical (A) to basal (B) axis of a cell (represented in d by red line). For every such plot of average fluorescence shown in this paper, each dotted black line represents the average of a minimum of 10 cells per embryo. The solid red line represents overall the average of six embryos. See Materials and methods for how quantifications were performed. Sharp peaks of Baz and E-Cad are seen at the apical side of the cell, with peaks for βPS integrins seen both apically and basally, with the basal peak of βPS slightly higher than the apical peak. (f–i)sna,twi mutants before EMT (stage 9; f), during migration (stage 11; g), and at stage 15 (h and i). In sna,twi double mutant embryos, Srp is expressed before EMT (f) and down-regulated by the start of germband retraction (stage 11; g), as in wild-type (a and b). (h) Stage 15 midgut cells in sna, twi mutants are rounded and multilayered. (i) Baz (i1), E-Cad (i2), and βPS (i3) do not localize as in wild-type (compare sna,twi, h and i, with wild-type, c and d). (j) Plots of the average fluorescence intensity across sna,twi mutant midgut cells show that peaks of Baz, E-Cad are lost. While the basal peak of βPS is completely absent, the apical peak of βPS is still there. n = 6 embryos per condition (minimum 10 cells per embryo). The posterior midgut in (a, b, f, and g) is demarcated by dashed yellow lines, and Hindsight (Hnt, green) labels midgut cells. White dashed lines in a and h indicate the apical side of the midgut, and yellow lines, the basal. Red boxes in c and h depict the area of the midgut epithelium shown in d and i. Confocal images are oriented with the anterior to the left and posterior to the right. Scale bars, 10 µm (c, d, h, and i) and 50 µm (a, b, f, and g).

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