Time-lapse imaging of the medial migration of primordial germ cells (PGCs) at stages 16–17. PGCs and cell membranes are visualized by co-injection of DsRed nanos-3′UTR RNA and Lyn-Venus (membrane-associated GFP) RNA. PGCs (red cells) move from the marginal zone (left side) toward the embryonic body (right side) along with somatic cells (green cells) (Kurokawa et al., 2006).