Developmental regulation of locomotive activity in X enopus primordial germ cells

Primordial germ cells ( PGC s) arise in the early embryo and migrate toward the future gonad through species‐specific pathways. They are assumed to change their migration properties dependent on their own genetic program and/or environmental cues, though information concerning the developmental change in PGC motility is limited. First, we re‐examined the distribution of PGC s in the endodermal region of Xenopus embryos at various stages by using an antibody against Xenopus Daz‐like protein, and found four stages of migration, namely clustering, dispersing, directionally migrating and re‐aggregating. Next, we isolated living PGC s at each stage and directly examined their morphology and locomotive activity in cell cultures. PGC s at the clustering stage were round in shape with small blebs and showed little motility. PGC s in both the dispersing and the directionally migrating stages alternated between the locomotive phase with an elongated morphology and the pausing phase with a rugged morphology. The locomotive activity of the elongated PGC s was accompanied by the persistent formation of a large bleb at the leading front. The duration of the locomotive phase was shortened gradually with the transition from the dispersing stage to the directionally migrating stage. At the re‐aggregating stage, PGC s became round in shape and showed no motility. Thus, we directly showed that the locomotive activity of PGC s changes dynamically depending upon the migrating stage. We also showed that the locomotion and blebbing of the PGC s required F‐actin, myosin II activity and R ho A / Rho‐associated protein kinase (ROCK) signaling.