BUSCADOR RECOLECTA

(A) Proposed model for the forces exerted over BCs as they migrate. (B–D) Schematic drawing showing the consequences of altering the forces exerted over BCs on their migration. BC, border cell; BM, basement membrane; FC, follicle cell; NC, nurse cell., Peer reviewed

(A) Schematic drawings of an S9 egg chamber illustrating the mirrorGal4 pattern of expression (mirrGal4, pink) and the point of ablation in the basal side of FCs (blue bar). NCs are in gray, BCs in yellow, FCs in purple, and BM in blue. (B) Images of life S9 control mirrGal4 and mirr>AbiRNAi egg chambers expressing Resille-GFP before and after FCs bonds are ablated. Blue bars indicate points of ablation. (C) Quantification of initial velocity of vertex displacement of the indicated ablated bonds. (D) Schematic drawing of an S9 egg chamber illustrating the mirrGal4 pattern of expression (pink) and the point of ablation in the NCs (blue bar). (E) Images of life S9 egg chambers of the indicated genotypes before and after NC bonds are ablated. Blue bars indicate points of ablation. (F) Quantification of initial velocity of vertex displacement of the indicated ablated bonds. (G–H’) Stills taken from live imaging of migrating BCs from egg chambers of the indicated genotypes. Discontinuous yellow lines demarcate the region between the anterior border of the egg chamber and the oocyte anterior membrane. (I, J) Quantification of BC migration speed in the area anterior to (I) and at the (J) mirr expressing region. The statistical significance of differences was assessed with a t test, * P value < 0.05, ** P value < 0.01, and *** P value < 0.001. Horizontal and vertical lines indicate mean and SD, respectively. Scale bar in B, E, and G–H’, 5 μm, 10 μm, and 20 μm, respectively. The raw data underlying panels C, F, I, and J are available in S1 Data. BC, border cell; BM, basement membrane; FC, follicle cell; GFP, green fluorescent protein; NC, nurse cell., Peer reviewed

(A–B”) Stills taken from live imaging of migrating BCs from egg chambers of the indicated genotypes. (C, D) Quantification of BC migration speed in egg chambers of the indicated genotypes in the area anterior to (C) and at the (D) mirr expressing region. (E) Quantification of egg chambers with complete BC migration. The statistical significance of differences was assessed with a t test, * P value < 0.05. Horizontal and vertical lines indicate mean and SD, respectively. Scale bars in A” and B”, 20 μm. The raw data underlying panels C–E are available in S1 Data. BC, border cell; FC, follicle cell., Peer reviewed

(A) Position of ovaries within a Drosophila female (left) and schematic of Drosophila ovaries showing an ovariole and its egg chambers (right). BC, border cells; Oo, oocyte; NCs, nurse cells; FCs, follicle cells; StFCs, stretch FCs; BM, basement membrane. (B) Diagram of an ovariole showing stages 8, 9, and 10 egg chambers (S8–S10). Anterior is left, posterior right. (C) Three-dimensional diagram of a S9 egg chamber showing the migration of the BCs between the NCs. (D–G’) Stills taken from live imaging of migrating BCs from egg chambers of the indicated genotypes. Discontinuous yellow lines demarcate the region between the anterior border of the egg chamber and the oocyte anterior membrane. (H–J) Quantification of BC migration speed during the whole migratory process (H) and during the early (I) and late (J) phases in egg chambers of the indicated genotypes. The statistical significance of differences was assessed with a t test, ** P value < 0.01. Horizontal and vertical lines indicate mean and SD, respectively. Scale bars in A’, B’, C’ and D’, 20 μm. The raw data underlying panels H–J are available in S1 Data., Peer reviewed

The basement membrane (BM) is a specialized extracellular matrix (ECM), which underlies or encases developing tissues. Mechanical properties of encasing BMs have been shown to profoundly influence the shaping of associated tissues. Here, we use the migration of the border cells (BCs) of the Drosophila egg chamber to unravel a new role of encasing BMs in cell migration. BCs move between a group of cells, the nurse cells (NCs), that are enclosed by a monolayer of follicle cells (FCs), which is, in turn, surrounded by a BM, the follicle BM. We show that increasing or reducing the stiffness of the follicle BM, by altering laminins or type IV collagen levels, conversely affects BC migration speed and alters migration mode and dynamics. Follicle BM stiffness also controls pairwise NC and FC cortical tension. We propose that constraints imposed by the follicle BM influence NC and FC cortical tension, which, in turn, regulate BC migration. Encasing BMs emerge as key players in the regulation of collective cell migration during morphogenesis., Peer reviewed

(A–B’) Stills taken from live imaging of migrating BCs from egg chambers of the indicated genotypes. (C) Quantification of the migration defects in egg chambers of the specified genotypes. The statistical significance of differences was assessed with a t test, *** P value < 0.001. Horizontal and vertical lines indicate mean and SD, respectively. Scale bars in A’ and B’, 20 μm. The raw data underlying panel C are available in S1 Data., Peer reviewed

(A–D) S9 controls tjGal4, tj>LanB1RNAi, mirrGal4 and mirr>EHBP1mCh egg chambers stained with the F-actin marker Rhodamine-Phalloidin (F-actin, red) and the DNA marker Hoechst (blue). Arrows in A indicate the curvature of the membranes between an anterior (A) and an anterior central NC (Ca); between 2 central NCs -a Ca and a Cp (a posterior central NC); between a Cp and a posterior (P) NC and between a P NC and the oocyte membrane. (E, F) Quantification of the radius of curvature of A, Ca, Cp and P NCs in S9 egg chambers of the indicated genotypes. BC clusters are marked with a red circle. (G–I) Stills taken from live imaging of migrating BCs from egg chambers of the indicated genotypes. (J) Quantification of BC migration speed in egg chambers of the indicated genotypes. The statistical significance of differences was assessed with a t test. Horizontal and vertical lines indicate mean and SD, respectively. Scale bars in A–D and G–I’, 20 μm. The raw data underlying panels E, F, and J are available in S1 Data., Peer reviewed

(A–B’) Stills taken from live imaging of migrating BCs from egg chambers of the indicated genotypes. (C) Quantification of the migration defects in egg chambers of the specified genotypes. The statistical significance of differences was assessed with a t test, *** P value < 0.001. Horizontal and vertical lines indicate mean and SD, respectively. Scale bars in A’ and B’, 20 μm. The raw data underlying panel C and D are available in S1 Data., Peer reviewed

(A–D, G–J’) S9 egg chambers of the designated genotypes stained with anti-pSqh (red) and the DNA marker Hoechst (blue) showing pSqh levels in the NCs (A–D) and the BCs (G–J’). (E, F, K, L) Quantification of pSqh levels in the NCs (E, F) and in the BCs (K, L) of egg chambers of the specified genotypes. G’–J’ Magnifications of the white boxes in G–J. The statistical significance of differences was assessed with a t test, * P value < 0.05, ** P value < 0.01, and *** P value < 0.001. Horizontal and vertical lines indicate mean and SD, respectively. Scale bar in A, 20 μm. The raw data underlying panels E, F, K, and L are available in S1 Data., Peer reviewed

A–D) Schematic drawings of early S9 (A), middle S9 (B), late S9 (C), and S10 egg chamber illustrating the BCs (yellow), NCs (gray), FCs (purple), BM (green), and the point of ablation in the NCs (blue bar). (A’–D’) Images of life control egg chambers of the indicated developmental stages expressing Resille-GFP before and after NC bonds are ablated. Blue bars indicate points of ablation. (E) Schematic representation of an egg chamber and the point of ablation in NCs. (F, G) Quantification of the initial velocity of vertex displacement of the indicated ablated bonds. The statistical significance of differences was assessed with a t test, * P value < 0.05 and ** P value < 0.01. Horizontal and vertical lines indicate mean and SD, respectively. Scale bar in A’–D’, 10 μm. The raw data underlying panels F and G are available in S1 Data., Peer reviewed