P4.2 gene expression during early gestation embryos. In situ hybridization analysis was used to detect P4.2 expression in mouse embryos at E7.5 (A and B) and E8.5 days (C and D). Sagittal sections of embryos within the deciduas were hybridized with the P4.2 antisense riboprobe. (A and C) Bright-field illumination; (B and D) dark-field illumination. Upon examination of multiple embryo sections, P4.2-specific labeling was detected in erythroid cells in the early heart region and blood vessels (indicated by arrowheads in A and B). NT, neural tube. The blood islands (BI) of the visceral yolk sac (YS) in (C) and (D) also show P4.2 hybridization. Micrographs were taken with a 20× (A and B) or 40× (C and D) objective.