Fibronectin expression in human fetal female and male gonads during first and second trimester. (A-F) Fibronectin (green) expression in the mesenchymal compartment of developing female gonads (A, A’, B, B’, D, D’, E, E’) and male gonads (C, C’, F, F’) during first and second trimester. Germ cells (red) were identified by the early marker OCT4 (nuclear) and late marker VASA (cytoplasmic). The same secondary antibody was used to detect OCT4 and VASA, because the two proteins localize to different cellular compartments (nucleus and cytoplasm, respectively) and their expression can therefore be clearly distinguished. Red arrows point to the BM of the OSE, and white arrows point to the BM of blood vessels. Note that occasional autofluorescent red blood cells are visible as red/orange cells inside blood vessels. Scalebars are 100 μm.