Fig. 3

Cell rearrangements during pruning of type I and II.

Stills from time-lapse movies illustrating cell rearrangements in type I pruning with lumen collapse before cell rearrangements (A) and type II pruning with cell rearrangements before lumen collapse (B) in transgenic embryos Tg(fliep:GFF)^ubs3,(UAS:mRFP),(5xUAS:cdh5-EGFP)^ubs12. Cell–cell junctions are green (VE-cad-EGFP), and cell cytoplasm is red. Black-and-white pictures show respective channels alone. Key steps of pruning are shown. Green arrows mark multicellular contacts (cell–cell junction length), white arrows mark transcellular lumen, and grey dotted lines mark unicellular fragments without lumen. Asterisks mark nuclei of cells contributing to the branch. (A) Pruning type I. A small, lumenized branch is made of two cells connected by two parallel lines of junctions (1). Lumen collapses when the branch is still multicellular (2–3); after lumen collapse, cells move away from each other, and cell–cell contact surface shrinks, generating a nonlumenized, ajunctional segment (4). Eventually, only the last bridging cell remains (5, grey arrow) prior to final detachment (not shown). See also S8 and S9 Movies and S3 Fig. (B) Pruning type II. Cellular architecture of a multicellular branch (1) is simplified to a branch made mainly by two cells connected by parallel lines of junctions (2). Further cell rearrangements lead to the formation of a partially unicellular tube (3). The lumen eventually collapses (4), and the cell body migrates towards the left-side major branch (5) until only a last, narrow cell extension connects two major branches (6). See also S10 Movie. (C) A graph representing percentage of pruning type I (dark blue) and II (light blue) in all pruning events analyzed in transgenic embryos of Tg(fliep:GFF)^ubs3,(UAS:mRFP),(5xUAS:cdh5-EGFP)^ubs12 and TgBAC(kdrl:mKate-CAAX)^ubs16, respectively. Scale bar: 10 µm.