While the mouse sarcoma origin of Matrigel could limit its relevance in modeling the brain perivascular space, the primary components of Matrigel, including laminin, heparan sulfate proteoglycans, collagen IV and nidogen [41], are known to be essential components of brain germinal matrices, as well as the subendothelial cell basement membrane of the brain microvasculature [42]. This evidence concerns the gene CD44 and sarcoma.