A–C, H&E-stained marmoset ovaries showing that large antral follicles (LAF) can develop despite inhibition of Dll4. A, Ovary from a marmoset on d 10 of the luteal phase after treatment with an antibody to Dll4 on luteal d 0 and d 2. Note the presence of two large antral follicles (LAF), in marked contrast to the restricted follicular growth expected at this stage of the cycle (compare with Fig. 2A). B, Ovary from a control marmoset treated with Fc for the duration of the follicular phase. Note the emergence of three large antral follicles and a recently ovulated follicle (CL). C, Ovary after treatment with Dll4 antibody throughout the follicular phase showing emergence of large antral follicles. D–-F, High-power magnifications of the wall of a large antral follicle in respective ovaries shown in panels A–C dual stained with BrdU (black nuclei) and CD31 (red cytoplasm). Note that the development of the vasculature within the thecal wall, shown by CD31 and the proliferating endothelial cells (shown by green arrows) appears to be similar to the control despite treatment with Dll4 antibody. Proliferating cells (black nuclei) in the granulosa cell layer (g) are also evident in each LAF. Scale bar, 500 μm (A–C) and 50 μm (D–F). CL, Corpus luteum.