Fig. S4

Ssrp1a is required for cell survival. (A-F) Anti-cleaved Caspase-3 staining shows apoptosis in ssrp1a^s819 mutant livers, co-stained with anti-2F11. Wild-type show no significant apoptosis during liver formation (A,B,E), whereas dying cells are found in ssrp1as819 mutant endoderm and adjacent LPM starting around 48 hpf, and their number is significantly increased from 56 hpf (E). Loss of Tp53 partially rescues apoptosis in ssrp1a^s819 mutant livers and LPM (F). This indicates that in addition other cell death mechanisms are activated in Ssrp1a-deficient cells. Notably, this rescue is less efficient than in the forming eye (supplementary material Fig. S3M), suggesting tissue-specific responses. (G) Importantly, the overall number of liver cells is not altered in the ssrp1a^s819;tp53 mutants compared to ssrp1a^s819 embryos at 48 and 68 hpf. (H-K) At 96 hpf, the expression of Tp53 target genes mdm2 and p21 is strongly increased in ssrp1a^s819 mutants compared with controls. (L-O) Expression of ccne is already at 48 hpf severely reduced in ssrp1a^s819 mutants (M), whereas pcna levels are not significantly altered (O). A-D are confocal projections of ventral views, H-O are dorsal views; all anterior to the top. *P<0.05; ***P<0.0005, determined by unpaired Student’s t-test. Error bars represent s.d.