The MPGZ starts to form at the pre-trochophore stage. (A) Between 14-24 hpf, the cells of the MPGZ incorporate EdU, while the PGCs (green) lack EdU label (asterisks). (B) EdU positive nuclei are detectable in the MPGZ after incubation between 24-48 hpf. (C) EdU positive MPGZ cells are detectable in young worms incubated at 48-72 hpf. (D) Incubation between 72-96 hpf also yields EdU labeled nuclei in the MPGZ. A'-D': higher magnification of the MPGZ from the corresponding stages. Larvae are fixed at 6-7 dpf. EdU labeling: red. Immunohistochemistry against Vasa protein: green. Arrow and dashed line: MPGZ, asterisks, PGCs. The three larval segments are labeled C = cephalic segment, I, and II. Anterior is to the top. Images are merged stacks of confocal images. Scale bar corresponds to 50 μm in A-D, and 20 μm in A'-D'.