Abstract
Similar to many other organisms, zebrafish primordial germ cells (PGCs) are specified at a location distinct from that of gonadal somatic cells. Guided by chemotactic cues, PGCs migrate through embryonic tissues toward the region where the gonad develops. In this process, PGCs employ a bleb-driven amoeboid migration mode, characterized by low adhesion and high actomyosin contractility, a strategy used by other migrating cells, such as leukocytes and certain types of cancer cells. The mechanisms underlying the motility and the directed migration of PGCs should be robust to ensure arrival at the target, thereby contributing to the fertility of the organism. These features make PGCs an excellent model for studying guided single-cell migration in vivo. In this review, we present recent findings regarding the establishment and maintenance of cell polarity that are essential for motility and discuss the mechanisms by which cell polarization and directed migration are controlled by chemical and physical cues.
Highlights
Primordial germ cells (PGCs) are specified early in embryonic development, proceeding the specification of somatic gonadal cells, which occurs at a different position
The germ plasm is initially enriched at four positions at the cleavage planes of the first two cell divisions and cells that inherit it develop into PGCs (Yoon et al, 1997); from these positions, directed by guidance cues the motile PGCs migrate toward their final target (Doitsidou et al, 2002; Knaut et al, 2003)
Consistent with the idea that actin polymerization functions as a primary front determinant, inhibiting bleb formation, does not abrogate the generation actin brushes (Olguin-Olguin et al, 2021), but, as discussed below, these are less stable. This polarization cascade and its kinetics are identical for both ligand-independent polarization and chemokine-directed PGC polarization (Figures 1A,B). These findings indicate that the main role of the chemokine Cxcl12a is to bias the underlying self-organizing polarity cascade toward regions with higher concentrations of the chemokine
Summary
PGCs migrate through embryonic tissues toward the region where the gonad develops. In this process, PGCs employ a bleb-driven amoeboid migration mode, characterized by low adhesion and high actomyosin contractility, a strategy used by other migrating cells, such as leukocytes and certain types of cancer cells. The mechanisms underlying the motility and the directed migration of PGCs should be robust to ensure arrival at the target, thereby contributing to the fertility of the organism. These features make PGCs an excellent model for studying guided single-cell migration in vivo.
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