The prion-like protein Shadoo has been suggested to compensate for the lack of PrP in Prnp-knockout mice, explaining their lack of extreme phenotype. In adult mice, both PrP and Shadoo have shown overlapping expression patterns and shared functions [1]. Their expression in the mouse embryo has also been suggested to be complementary, as invalidation of both genes results in embryonic lethality [2]. The developmental expression profile of PrP has been described from post-implantation stages up until birth [3-5]. However the spatial expression pattern of Shadoo in the developing mouse embryo is not known. We previously described the expression profile of the prion-like protein Shadoo in adult mice using Sprn reporter mice (Sprn-GFP and Sprn-LacZ). Here we used these mice to describe the developmental expression of Shadoo between 10.5 and 14.5 dpc. The observed pattern in specific embryonic cell lineages and in extra-embryonic tissues is consistent with the previously reported phenotype resulting from its knockdown. (C) 2011 Elsevier Inc. All rights reserved.