Pericyte recruitment to microvascular tubes during vasculogenesis in quail CAMs correlates with basement membrane matrix assembly. (A) Quail CAMs were isolated at 5 and 7 days of development and fixed for detergent-free immunostaining. Images reveal basement membrane deposition (arrowheads) around developing microvessels at the 7-day time point. Bars equal 10 μm. (B-C) Double staining of quail CAMs at 7 days for QH1, an EC-specific marker in red, versus SMA, recognizing pericytes at the microvascular level in green. (B) Reveals the coassociation of the 2 cells at this time point. (C) Staining of SMA (in green) versus the basement membrane component protein, fibronectin (in red), reveals the location of the pericytes in relation to the basement membrane. (D-E) Electron microscopy of quail CAMs reveals a continuous basement membrane (arrows) along the ablumenal surface of developing microvessels and between the perivascular cells (closed arrowheads) and the endothelium (open arrowheads). Bar equals 2 μm.