Blood Vessels/physiology; CD146 Antigen/metabolism; Hematopoietic Stem Cells/metabolism; Hematopoietic Stem Cells/physiology; Adult; Animals; Antigens, CD34/metabolism; Blood Vessels/cytology; Blotting, Western; Calcium-Binding Proteins/genetics; Calcium-Binding Proteins/metabolism; Cell Communication; Cells, Cultured; Chemokine CXCL12/genetics; Chemokine CXCL12/metabolism; Coculture Techniques; Fetal Blood/cytology; Fetal Blood/metabolism; Hematopoietic Stem Cells/cytology; Humans; Immunohistochemistry; Intercellular Signaling Peptides and Proteins/genetics; Intercellular Signaling Peptides and Proteins/metabolism; Intermediate Filament Proteins/genetics; Intermediate Filament Proteins/metabolism; Membrane Proteins/genetics; Membrane Proteins/metabolism; Mesenchymal Stem Cells/cytology; Mesenchymal Stem Cells/metabolism; Mesenchymal Stem Cells/physiology; Mice; Nerve Tissue Proteins/genetics; Nerve Tissue Proteins/metabolism; Nestin; Receptors, Notch/genetics; Receptors, Notch/metabolism; Reverse Transcriptase Polymerase Chain Reaction; Serrate-Jagged Proteins