Positive correlation between relative mRNA expression of PRNP and SPRN in cerebral and cerebellar cortex of sheep.

SPRN is an interesting new member of the PRNP family because of its sequence homology with the hydrophobic region of PRNP, its expression in brain tissue and its PrP-like properties in functional experiments on Prnp(0/0) mice. In this study, we investigated by quantitative real-time PCR the relative mRNA expression levels of SPRN and PRNP in sheep cerebrum and cerebellum and the mutual relationship between these expression levels. Analysis of PRNP and SPRN mRNA expression levels in 45 cerebral cortex and 47 cerebellar cortex samples showed that the PRNP expression level was significantly higher (p<0.05) in cerebellum than in cerebrum, while no significant difference was detected for SPRN between these tissues. The expression level varied clearly more in cerebrum than in cerebellum for both genes tested, and the variation was larger for SPRN than for PRNP in both types of brain tissue. Remarkably, the mRNA expression levels of PRNP and SPRN showed a highly significant positive correlation in both cerebrum (p<0.0001) and cerebellum (p<0.001). This positive correlation might indicate co-regulation between these genes. Further investigation on the causal nature of this correlation may provide new insights into prion pathogenesis.