The transcription factor ERG is down-regulated in constricted hyaloid vessels. (A) Flat-mount hyaloid vessels from a P6 wild-type mouse immunostained for Isolectin-B4 (red) and ERG (green). Arrows indicate a constricted hyaloid vessel with reduced nuclear ERG expression. (Scale bar, 100 µm.) (B, Top) Flat-mount hyaloid vessels from a P8 wild-type mouse immunostained for Isolectin-B4 (red), ERG (gray), and TUNEL (green). (B, Bottom) Magnified views of region outlined in white. The white arrow demonstrates down-regulation of ERG in a constricted hyaloid vessel that is not yet TUNEL+. The yellow arrow indicates a highly constricted, apoptotic vessel with irregular, nonnuclear ERG expression. (Scale bar, 50 µm.) (C) Immunostained cross-section of an eye from a P8 wild-type mouse allowing comparison of ERG expression (green) between retinal and hyaloid ECs that are stained with Isolectin-B4 (red); nuclei are counterstained with DAPI (blue). (Insets) The solo ERG channel for hyaloid (Top) and retinal (Bottom) ECs demonstrates the absence of ERG expression in regressing hyaloid ECs. (Scale bar, 50 µm.)