Oct4 Is Required ∼E7.5 for Proliferation in the Primitive Streak
Figure 2
Depletion of Oct4 ∼E7.5 results in diminished viability, reduced mesenchyme density and broader spacing between the neural folds.
A The fraction (Oct4f/f;CreERT2+/−/total) embryos recovered at each developmental stage (‘@’ indicates resorbing embryos). Embryos were administered tamoxifen ∼E7.0 and ∼E7.5 (Table S1M–O). B,C Representative images of an E10.5 Oct4f/f;CreERT2+/− embryo and Oct4f/f littermate following tamoxifen administration ∼E7.0 and ∼E7.5. Features such as the otic cup (∧) and forelimb bud (#) which normally arises after NTC is initiated and turning is complete are present in both Oct4f/f;CreERT2+/− and Oct4f/f littermates. Conversely, defects in turning, somitogenesis, neural tube closure and posterior extension all fail to recover in Oct4f/f;CreERT2+/− embryos by E10.5. Scale bars in ‘B,C’ are 250 µm. B Sagittal view. C Dorsal view. D Schematic illustrating NT closure points, the directions in which the NT ‘zippers’ shut as well as the sections where mesenchyme density was quantified. E,F Representative Hematoxylin and Eosin (H and E) sections from the trunk (see ‘Tr’ in panel ‘D’) ∼E9.5. Differences in the density of mesenchyme, which is indicated with two-headed arrows, are apparent. Embryos were administered tamoxifen ∼E7.0 and ∼E7.5 and dissected ∼E9.5 (Table S1M–O). Scale bars in E,F are 50 µm. E Oct4f/f F Oct4f/f;CreERT2+/−. G Mesenchyme, connective tissue comprised of mesoderm and neural crest cells, has a lower density in Oct4COND MUT. The average density within 4×10−2 mm2 ±s.e.m. (200 µm×200 µm) from sections equivalent to those in panel ‘E,F’ is plotted (F1,13 = 54.60, p<0.05 2-way ANOVA, *p<0.05, ***p<0.001 Bonferroni posttest). Due to the posterior truncation, insufficient mesenchyme was present in the tail of Oct4COND MUT to quantify. H–J The neural tube in H Oct4f/f I Oct4f/f;CreERT2+/−. Scale bars in ‘H,I’ are 100 µm. J The distance between neural folds in the trunk of Oct4f/f;CreERT2+/− is broader (F2,22 = 17.42, p<0.05 2-way ANOVA, **p<0.01 Bonferroni posttest. Embryos in ‘H–J’ were administered tamoxifen ∼E7.0 and ∼E7.5 and dissected ∼E9.5 (Table S1M–O).