Early embryonic lethality in constitutive Ssb1/Ssb2 double knockout (DKO) mice and acute mortality in conditional Ssb1/Ssb2 double knockout (cDKO) mice due to BM failure and small intestine atrophy. (A) Embryos at E7.5 (upper panel; scale bar = 200 μm) and E10.5 (lower panel, scale bar = 1 mm) from Ssb1^+/−;Ssb2^−/− intercrossed, timed matings. (B) Histologic analyses of resorbed embryos from E10.5. Apoptotic bodies are indicated by black arrows. Images were acquired at ×1 (top) and ×40 (bottom) magnification. (C) Body weight change on day 7 of TAM-induced adult Ctrl and cDKO mice. (D) Representative images of spleen and thymus recovered from Ctrl and cDKO mice on day 7 postinduction with TAM (1 mg/day by IP injection for 5 consecutive days). (E) H&E staining of small intestine sections. Images were acquired on day 7 postinduction at ×20 (left) magnification and zoomed in ×16 for indicated areas (right). (F) H&E staining of BM sections. Images were acquired on day 7 postinduction at ×4 (left) and ×20 (right) magnifications. (G) BM cell count. (H-I) Leukocyte and hematocrit counts in peripheral blood (PB) from Ctrl and cDKO mice on day 7 postinduction with TAM (1 mg/day by IP injection for 5 consecutive days). Statistical analysis represents t test. Each point represents an individual mouse/biological replicate. See also supplemental Figure 1. *P < .05; **P < .01; ***P < .001; ****P < .0001.