Expression and knockdown of cellular prion protein (PrPC) in differentiating mouse embryonic stem cells

The mammalian cellular prion protein (PrPC) is a highly conserved glycoprotein that may undergo conversion into a conformationally altered isoform (scrapie prion protein or PrPSc), widely believed to be the pathogenic agent of transmissible spongiform encephalopathies (TSEs). Although much is known about pathogenic PrP conversion and its role in TSEs, the normal function of PrPC is poorly understood. Given the abundant expression of PrPC in the developing mammalian CNS and the spatial association with differentiated stages of neurogenesis, recently it has been proposed that PrPC participates in neural cell differentiation. In the present study, we investigated the role of PrPC in neural development during early embryogenesis. In bovine fetuses, PrPC was differentially expressed in the neuroepithelium, showing higher levels at the intermediate and marginal layers where more differentiated states of neurogenesis were located. We utilized differentiating mouse embryonic stem (ES) cells to test whether PrPC contributed to the process of neural differentiation during early embryogenesis. PrPC showed increasing levels of expression starting on Day 9 until Day 18 of ES cell differentiation. PrPC expression was negatively correlated with pluripotency marker Oct-4 confirming that ES cells had indeed differentiated. Induction of ES cells differentiation by retinoic acid (RA) resulted in up-regulation of PrPC at Day 20 and nestin at Day 12. PrPC expression was knocked down in PrP-targeted siRNA ES cells between Days 12 and 20. PrPC knockdown in ES cells resulted in nestin reduction at Days 16 and 20. Analysis of bovine fetuses suggests the participation of PrPC in neural cell differentiation during early embryogenesis. The positive association between PrPC and nestin expression provide evidence for the contribution of PrPC to ES cell differentiation into neural progenitor cells.