Recently, a novel gene encoding a prion protein (PrP)-like glycoprotein, PrPLP/Dpl, was identified as being expressed ectopically by neurons of the ataxic PrP-deficient (Prnp(-/-)) mouse lines exhibiting Purkinje cell degeneration In adult wild-type mice, PrPLP/Dpl mRNA was physiologically expressed at a high level by testis and heart, but was barely detectable In brain. However, transient expression of PrPLP/Dpl mRNA was detectable by Northern blotting in the brain of neonatal wild-type mice, showing maximal expression around 1 week after birth. In situ hybridization paired with immunohistochemistry using anti-factor VIII serum identified brain endothelial cells as expressing the transcripts. Moreover, in the neonatal wild-type mice, the PrPLP/Dpl mRNA colocalized with factor VIII immunoreactivities in spleen and was detectable on capillaries in lamina propria mucosa of gut, These findings suggested a role of PrPLP/Dpl in angiogenesis, in particular blood-brain barrier maturation in the central nervous system Even in the ataxic Ngsk PrnP(-/-) mice, the physiological regulation of PrPLP/Dpl mRNA expression In brain endothelial cells was still preserved. This strongly supports the argument that the ectopic expression of PrPLP/Dpl in neurons, but not deregulation of its physiological expression in endothelial cells, is involved In the neuronal degeneration in ataxic Prnp-/- mice.