Mikiko INAKI1, Smitha VISHNU, Adam CLIFFE, and Pernille RØRTH
Institute of Molecular and Cell Biology, Singapore 138673
1 - Present address: Mechanobiology Institute, National University of Singapore, Singapore 117411.
Published in PNAS 23 January 2012 (Epub ahead of print.)
Directed cell migration is important for normal animal development and physiology. The process can also be subverted by tumor cells to invade other tissues and to metastasize. Some cells, such as leukocytes, migrate individually; other cells migrate together in groups or sheets, called collective cell migration. Guidance of individually migrating cells depends critically on subcellularly localized perception and transduction of signals. For collective cell migration, guidance could result from cells within a group achieving different signaling levels, with directionality then encoded in the collective rather than in individual cells. Here we subject this collective guidance hypothesis to direct tests, using migration of border cells during Drosophila oogenesis as our model system. These cells normally use two receptor tyrosine kinases (RTKs), PDGF/VEGF-related receptor (PVR) and EGFR, to read guidance cues secreted by the oocyte. Elevated but delocalized RTK signaling in one cell of the cluster was achieved by overexpression of PVR in the absence of ligand or by overexpression of fusion receptors unable to detect Drosophila ligands; alternatively, Rac was photoactivated centrally within a single cell. In each case, one cell within the group was in a high signal state, whereas others were in low signal states. The high signal cell directed cluster movement effectively. We conclude that differences in cell signaling states are sufficient to direct collective migration and are likely a substantial contributor to normal guidance. Cell signaling states could manifest as differences in gene expression or metabolite levels and thus differ substantially from factors normally considered when analyzing eukaryotic cell guidance.
Fig. 1. A single border cell expressing PVR–GFP directs cluster movement in
the absence of ligand. (A) Schematic of a stage 9 egg chamber (section), germ
line cells outlined in red. Border cells move left to right (oocyte). (B) Schematics
of border cell clusters. (Upper) Proposed collective guidance mechanisms
(12, 13). (Lower) Experimental approach used in this study. (C–E) Still
images from three movies with one PVR–GFP positive border cell (green); all
cells are outlined by red FM4-64 dye. Clusters are initiating forward movement
(C) (Movie S1), rotating at start (D) or taking abnormal “side” route (E)
(Movie S2). (F) Outline of how cell position and cluster movement were
quantified: yellow, cell in front; blue, cell in back. Examples shown in C–E are
not free clusters and could not be used; Movie S3 shows one quantified movie
section. (G) Forward speed (X-direction only, toward oocyte) to the next time
point for the center of the cluster according to the position of the PVR–GFP
positive cell. A total of 296 time points were scored from 11 different clusters;
SEM is indicated; the difference between forward speed for front versus side
position and for back versus side position are highly significant (P < 0.001).
(H–H′′) Three time points from Movie S4 showing one high PVR cell exploring
in all directions. Genotype for all panels: Pvf11624, hs-FLP/Pvf11624; slbo-flipout-
EGFR-RNAi/+; c522 (Gal4), FRT82, tub-Gal80/FRT82, UAS-PVR-GFP.
For more information on Pernille RØRTH’s research, please click here.