Abstract
The mammalian cellular prion protein (PrP(C) ) is a highly conserved glycoprotein that may undergo conversion into a conformationally altered isoform (scrapie prion protein or PrP(Sc) ), widely believed to be the pathogenic agent of transmissible spongiform encephalopathies (TSEs). Although much is known about PrP(Sc) conversion and its role in TSEs, the normal function of PrP(C) has not been elucidated. In adult mammals, PrP(C) is most abundant in the central nervous tissue, with intermediate levels in the intestine and heart, and lower levels in the pancreas and liver. PrP(C) is expressed during neurogenesis throughout development, and it has recently been proposed that PrP(C) participates in neural cell differentiation during embryogenesis. In order to establish the developmental timing and to address the cell-specific expression of PrP(C) during mammalian development, we examined PrP(C) expression in bovine gametes and embryos through gestation Day 39. Our data revealed differential levels of Prnp mRNA at Days 4 and 18 in pre-attachment embryos. PrP(C) was detected in the developing central and peripheral nervous systems in Day-27, 32-, and -39 embryos. PrP(C) was particularly expressed in differentiated neural cells located in the marginal regions of the central nervous system, but was absent from mitotically active, periventricular areas. Moreover, a PrP(C) cell-specific pattern of expression was detected in non-nervous tissues, including liver and mesonephros, during these stages. The potential participation of PrP(C) in neural cell differentiation is supported by its specific expression in differentiated states of neurogenesis.