Fig. 2. Primordial germ cells express the Pin1 protein. (A) Immunohistochemistry using anti-Pin1 antibodies reveals high Pin1 protein expression in postnatal day 1 (P1) gonocytes (arrows). (B) No Pin1 protein is detected in Pin1^-/- gonocytes (arrow). (C,E) Immunofluorescence shows intense Pin1 protein expression (green) in 13.5 dpc male XY (C) and female XX (E) PGCs, identified as large round cells by their surface antigen PECAM (red, round cells). (D,F) Negative control using pre-absorbed anti-Pin1 antibodies with Pin1 proteins shows the lack of green Pin1 staining, demonstrating the specificity of the anti-Pin1 antibody. (G) Immunostaining for Pin1 in 9.5 dpc embryo section reveals Pin1 expression (green) in the embryo. (H) Alkaline phosphatase detection of PGCs (brown, arrowhead) in the adjacent serial-section shows the location of PGCs in the hindgut (hg) at 9.5 dpc. Pin1 protein (green) is expressed in the PGC containing regions of the hindgut in G. (I) Negative control using pre-absorbed anti-Pin1 antibodies shows the lack of green Pin1 staining. (G,I) Red, DAPI stained nuclei. s, somite.