Date Published: February 26, 2019
Publisher: Public Library of Science
Author(s): Mohammad Goudarzi, Aleix Boquet-Pujadas, Jean-Christophe Olivo-Marin, Erez Raz, Klemens Rottner.
Blebs are cellular protrusions observed in migrating cells and in cells undergoing spreading, cytokinesis, and apoptosis. Here we investigate the flow of cytoplasm during bleb formation and the concurrent changes in cell volume using zebrafish primordial germ cells (PGCs) as an in vivo model. We show that bleb inflation occurs concomitantly with cytoplasmic inflow into it and that during this process the total cell volume does not change. We thus show that bleb formation in primordial germ cells results primarily from redistribution of material within the cell rather than being driven by flow of water from an external source.
Cell migration is instrumental during normal development and for homeostasis in the adult organism [1–4]. When misregulated, cell migration is associated with pathological conditions such as inflammation and cancer cell metastasis [5, 6]. Understanding the cellular events contributing to the migration of cells is thus of general interest in biology and medicine. At the biophysical level, the precise mechanisms contributing to translocation of the cell body, a process accompanied by shape changes and flow of material, are not fully understood. Cells employ two main migration strategies, with certain cell types capable of alternating between two migration modes [7–9]. In the first mode of migration, cells make use of actin polymerization at the cell front as a means for pushing the membrane forward . The other migration strategy, used by different cell types including zebrafish primordial germ cells (PGCs) involves the formation of blebs as a mean for translocation of the cell body [11–15].
Our experiments reveal that the cytoplasm flow patterns are consistent with the idea that redistribution of material within the cell is responsible for bleb growth, while the volume of migrating PGCs is not significantly altered during the course of bleb formation; we could not find evidence supporting the notion that Aqp proteins are directly involved in bleb formation. Cellular blebbing is a common process utilized by migrating cells, but it is also found in a range of other processes such as apoptosis , generation of lumen in the vascular system , cytokinesis and cell spreading . We consider it very likely that our findings, supporting the idea that blebs are powered by internal translocation of material, are relevant for those other contexts where blebs are found, as well as in contexts of other migration modes.