Fig. 4 |. PAC integration involves basally directed growth of a transitional SJ with distinct apical EC–EC and basal PC–EC zones.

Volumetric images were analysed from midguts that expressed Su(H)-lacZ and an apical marker (moeABD::GFP or mdu::GFP) and that were immunostained for β-gal and an SJ marker (Ssk or Tsp2a). Cells were randomly selected from across eight guts in two independent experiments. Full genotypes are in Supplementary Table 1. a, Cartoon of the three SJ parameters measured at each integration stage (St): λ, SJ_EC–EC length; ψ, SJ_PC–EC length; δ, distance from the basal edge of the SJ to the basal epithelium. Apical membrane, cyan; SJ_EC–EC, yellow; SJ_PC–EC, orange; progenitor cell (Su(H)-lacZ⁺ enteroblast or pre-enterocyte), blue; mature neighbour enterocytes, grey. For measurement details, see Methods. In stage 4 depiction, dashed yellow line represents SJ_EC–EC that is out-of-plane of the drawing. b–f, Raincloud plots (violin plot on left; box plot on right) show the indicated measurements for SJs associated with stage 1–5 progenitor cells (blue; n = 30 SJs for each stage): total length of SJ associated with progenitor cell (λ + ψ) (b); length of SJ_EC–EC (λ) (c); length of SJ_PC–EC (ψ) (d); SJ_PC–EC as percentage of SJ_Total (ψ/(λ + ψ) × 100) (e). f, Distance from basal edge of the SJ to the basal epithelium (δ). Box plots display median as centre line, the bounds of the box represent the first and third quartiles, whiskers show the minimum and maximum values shown by whiskers, and diamonds indicate outliers (N = 7 guts; n = 150 progenitor cells). g, Cartoons show 3D structure of transitional stage 2–4 SJs as defined by b–f. Apical membrane (cyan), progenitor cell (blue) and mature neighbour enterocytes (grey), apical SJ_EC–EC (yellow) and basal SJ_PC–EC (orange). During stages 2–4, the basal SJ_PC–EC expands at the expense of the apical SJ_EC–EC during a basal-to-apical neighbour exchange.