(A and B) Paraffin sections of (A) proliferative IH (from 6-mo-old child) and (B) involuted IH (from 44-mo-old child) were labeled with immunofluorescent antibodies to endothelial CD31 and IH endothelial GLUT-1. Overlaid DAPI images indicate GLUT-1⁺CD31⁺ endothelial cells. On adjacent sections, in situ hybridization probes to endothelial miR-126a-3p and C19MC miR-517a/c-3p indicate that normal CD31⁺GLUT-1^– endothelium (white arrows) contains miR-126a-3p but not miR-517a/c-3p, while CD31⁺GLUT-1⁺ tumor endothelium (yellow arrows) contains both miR-126a-3p and miR-517a/c-3p. A scrambled miR probe was used as a negative control; nuclei were stained with Fast Red. Scale bar: 100 μm (middle); 50 μm (bottom). (C) In situ hybridization images of sections from placenta demonstrate miR-517a/c-3p in the placental trophoblast (black arrows). miR-517a/c-3p and miR-126a-3p were detected in villous endothelial cells (magenta arrows). Scale bar: 200 μm (top); 50 μm (bottom). (D) FACS and qRT-PCR analysis of a proliferative IH confirmed GLUT-1⁺CD31⁺ cells as the miR-517–expressing cell type. A single-cell suspension from proliferative IH was labeled with GLUT-1^–EGFP and CD31-PE antibodies and sorted into GLUT-1⁺CD31⁺ and GLUT-1^–CD31^– populations. RNA isolation and qRT-PCR analysis of these sorted populations demonstrates enriched miR-517a-3p expression in the GLUT-1⁺CD31⁺ population. The y axis represents relative mRNA or miRNA compared with levels of GAPDH or RNU48, respectively. Data points on the qRT-PCR graphs indicate duplicate samples prepared at the sorting stage from the same lesion, and error bars represent standard deviations.