Fig. 4. Two meiotic markers, SYN/COR (A) and H2AX (B), are expressed in an anterior to posterior pattern in 13.5-15.5 dpc XX gonads: SYN/COR and H2AX (green); germ cells and vasculature (PECAM-1, red). A higher magnification of the region surrounded by the white rectangle is shown below the corresponding image. Consecutive 8 µm sections were stained with each antibody to define the spatial relationship between SYN/COR and H2AX. Arrows indicate the leading front of staining at 14.5 dpc. Arrowheads indicate the first detection of SYN/COR at 13.5 dpc and the filamentous pattern associated with the assembly of homologous chromatid pairs in zygotene/pachytene at 14.5 dpc. A, anterior; P, posterior.