Human astrocytes, defined as EGFP+/hGFAP+/hNuclei+, regularly extended processes that terminated in end-feet contiguously arrayed along blood vessel wall (Fig. 2A-B). Their long processes were often tortuous, and resembled the processes of interlaminar astroglia, a phenotype previously described only in adult human and ape brain (Oberheim et al., 2006) (Fig. 2C); these cells are characterized by long, unbranched processes that traverse multiple cortical laminae (Colombo, 2001). Many of the engrafted human astrocytes in chimeric mice extended processes that spanned >0.5 mm (Fig. 2D). A large number of mitochondria were present in the long processes (Fig. 2E). Other engrafted human cells exhibited the long, varicosity-studded processes of varicose projection astrocytes, a second class of hominid astrocytes (Oberheim et al., 2009).
