Fig. 1: Natural removal of Z-DNA in germ cells of the mouse foetus.

Immunohistochemistry images of testis samples are shown from male mouse foetuses. a, Z-DNA antibody staining (green) is diminishing in germ cells, as identified by PGC7 staining (red) at 13.5, 15.5 and 18.5 dpc. Scale bars, 5 µm. b,c, Loss of Z-DNA is specific to the germ cells in the foetal testis. Immunohistochemistry is shown for foetal testis sections at 13.5, 15.5 and 18.5 dpc timepoints, using Z-DNA antibody (green), germ cell marker (PGC7) and DAPI counterstain. Merged images are displayed on the right. Prospermatogonia (b) exhibit loss of Z-DNA. Somatic cells (c) maintain Z-DNA. Scale bars, 1 µm. d, ZBTB43 protein is detected in germ cells inside the testicular cords of the wild-type but not in the Zbtb43^−/− mutant testis at 15.5 dpc. Note the typical weak and diffuse DAPI staining of germ cell nuclei. The surrounding Sertoli cells, which exhibit stronger DAPI staining, are negative for ZBTB43 staining. Scale bars, 5 µm. e, Double staining of 15.5 dpc germ cells with ZBTB43 and germ cell marker OCT4 antibodies is shown in testis samples at 15.5 dpc. Scale bars, 2 µm. f, Double staining of testis samples using the ZBTB43 and germ cell marker DDX4 antibodies is shown at the foetal days as marked. Scale bars, 2 µm. The results shown represent three independent immunostaining experiments using four biologically independent testis samples per experiment (a–c), five independent experiments using three biologically independent testis samples per experiment (d), one immunostaining experiment using two biologically independent testis samples (e) and two independent immunostaining experiments using two biologically independent testis samples per experiment (f).