S-phase DNA damage checkpoint activation is intact in <i>ztf-8</i> mutants.

<p><b>A</b>. <i>ztf-8</i> mutants exhibit enlarged nuclear diameters at the premeiotic tip. Asterisks indicate statistical significance by the two-tailed Mann-Whitney test, 95% C.I., P<0.0001 without HU treatment and P<0.0001 in 20 mM HU containing NGM media. n = 178, 170, 80, 81 for wt, <i>ztf-8</i>, wt+HU, and <i>ztf-8</i>+HU, respectively. <b>B</b>. Immunolocalization of ATL-1 in premeiotic tip nuclei of germlines from IR or non-IR treated wild type worms and <i>ztf-8</i> mutants. <b>C</b>. Immunostaining for phospho CHK-1 (pCHK-1) of germline nuclei at the indicated stages. Bar, 2 µm. <b>D</b>. 69% of mitotic germline nuclei in <i>ztf-8</i> mutants exhibit PCN-1 signal, which marks nuclei in S-phase, compared to 93% of nuclei in wild type. Arrows indicate nuclei lacking PCN-1 signal. Wild type worms exposed to 5 mM HU were used as a control for S-phase arrest. Bar, 2 µm. <b>E</b>. Quantitation of the percentage of nuclei containing PCN-1 signal. Asterisks indicate statistical significance. P = 0.0002 for wild type and wild type+HU and P = 0.0088 for wild type and <i>ztf-8</i> mutants. Statistical tests by the two-tailed Mann-Whitney test, 95% C.I.