Abstract
SummaryThe directional migration of primordial germ cells (PGCs) to the site of gonad formation is an advantageous model system to study cell motility. The embryonic development of PGCs has been investigated in different animal species, including mice, zebrafish, Xenopus and Drosophila. In this study we focus on the physical properties of Xenopus laevis PGCs during their transition from the passive to the active migratory state. Pre-migratory PGCs from Xenopus laevis embryos at developmental stages 17–19 to be compared with migratory PGCs from stages 28–30 were isolated and characterized in respect to motility and adhesive properties. Using single-cell force spectroscopy, we observed a decline in adhesiveness of PGCs upon reaching the migratory state, as defined by decreased attachment to extracellular matrix components like fibronectin, and a reduced adhesion to somatic endodermal cells. Data obtained from qPCR analysis with isolated PGCs reveal that down-regulation of E-cadherin might contribute to this weakening of cell-cell adhesion. Interestingly, however, using an in vitro migration assay, we found that movement of X. laevis PGCs can also occur independently of specific interactions with their neighboring cells. The reduction of cellular adhesion during PGC development is accompanied by enhanced cellular motility, as reflected in increased formation of bleb-like protrusions and inferred from electric cell-substrate impedance sensing (ECIS) as well as time-lapse image analysis. Temporal alterations in cell shape, including contraction and expansion of the cellular body, reveal a higher degree of cellular dynamics for the migratory PGCs in vitro.
Highlights
As germ cell specification takes place in a region different from the site of gonad formation, primordial germ cells (PGCs) have to migrate in a directional manner during embryogenesis
In this study we focus on the physical properties of Xenopus laevis PGCs during their transition from the passive to the active migratory state
Using single-cell force spectroscopy, we observed a decline in adhesiveness of PGCs upon reaching the migratory state, as defined by decreased attachment to extracellular matrix components like fibronectin, and a reduced adhesion to somatic endodermal cells
Summary
As germ cell specification takes place in a region different from the site of gonad formation, PGCs have to migrate in a directional manner during embryogenesis. In Xenopus laevis, germ cells are specified by inheriting maternal determinants that are part of the germ plasm. As a result of directional transport during oogenesis, this material localizes to the vegetal pole of the fertilized egg which contains a set of specific vegetally localizing mRNA known to be essentially involved in germ cell specification and migration (Berekelia et al, 2005). Followed by passive movement together with the surrounding endodermal cells during gastrulation, PGCs start to migrate actively within the endoderm at tailbud stages. Via a thin strip of connective tissue called dorsal mesentery, PGCs travel to the dorsal body wall where they associate with somatic gonadal cell precursors. The primordial germ cells form germ line stem cells, which differentiate into the gametes (Heasman et al, 1977; Molyneaux and Wylie, 2004; Wylie et al, 1976; Wylie and Heasman, 1976)
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