ECs and HCs have cytoplasmic continuity in the VA. (A) Electron microscopy of 2 independent VA clusters at lower (left panels) and higher magnification (right panels) revealed close EC and HC interactions (top and bottom panels). Certain areas of EC-HC contact appear devoid of any cytoplasmic boundaries (arrows). In addition, the HCs are in a proliferative state, as suggested by the condensed chromatin and mitotic appearance of the nuclei (asterisks). (B) Higher magnification demonstrates the loss of boundaries in EC-HC associations of the VA (arrows, left 2 panels). N indicates the nucleus of the EC. We also found cases where intact boundaries were also noted (arrowheads, rightmost panel).