Fig. 3. Zygotically transcribed genes are essential for PGC polarization and motility. (A) Embryos treated with -amanitin (lower panels) exhibit gastrulation defects, most pronounced is the inhibition of epiboly (arrowheads). (B) Transcription of the zygotically expressed genes [represented here by RT-PCR analysis for no tail (ntl)] is inhibited by -amanitin (lower panel) whereas the level of maternally provided transcripts [represented here by RT-PCR analysis for vasa (vas)] is unaffected. (C) Snapshots from low-magnification time-lapse movies recorded over 2 hours of zebrafish development showing a representative PGC cluster. The germ cells in control embryos (upper panels, one cell labelled with an asterisk) migrate actively and leave the cluster following the transition whereas PGCs in -amanitin treated embryos (lower panels) remain clustered and immotile. (D) Snapshots from high-magnification time-lapse movies of control (upper panels) and -amanitin treated PGCs (lower panels). PGCs treated with -amanitin remain arrested in the second phase of their differentiation extending protrusions in all directions and fail to polarize (supplementary material Movies 8 and 9). (E) Snapshots from high-magnification time-lapse movies. 12 hpf old wild-type PGCs transplanted into an -amanitin treated host embryo are not able to migrate relative to host cells, but show cell morphology characteristic of cells of their age. (F) 7 hpf old -amanitin treated PGCs transplanted into a 5.3 hpf wild-type host remain arrested in the second phase of their maturation displaying extensions in all directions and fail to polarize and migrate. The apparent movement of the cluster in the lower panels is a result of passive movement together with somatic cells. (G) At 4.3 hpf, Dead end knockdown (dnd-MO) PGCs behave like wild-type cells of a similar age. At 4.7 hpf, dnd-MO treated germ cells do not polarize and migrate but are capable of extending small protrusions and divide (supplementary material Movies 10 and 11). Bars, 10 µm.