According to Bruns et al. , a fully developed murine yolk sac can be morphologically divided into 5 regions: juxtauterine, periplacental, villous, smooth visceral, and in-traplacental yolk sac, the endodermal layers of which are derived from either parietal or visceral endoderm of the pre-gastrulating embryo. While PDGFRot is expressed in both endodermal layers of pre-gastrulating embryos, in this study we found that its expression becomes restricted to juxtauterine, periplacental, and intraplacental yolk sac endoderm in mature yolk sac. This is the first study to show that the IPY in the yolk sac region expresses high levels of PDGFRa after 11.5 dpc. buy levaquin online
Morphologically, the squamous and columnar epithelial cells of the IPY appear to be derived from parietal and visceral endoderm, respectively. Selective expression of calbindin-D9k in columnar cells of the IPY and visceral yolk sac further supports this notion and suggests that calbindin-D9k serves as a lineage marker for visceral endoderm. In contrast to the lineage-specific expression of calbindin-D9k, PDGFRa is expressed in both types of epithelium of the IPY, and its expression appears to correlate more with the embryonic stage than with cell lineage. Interestingly, PDGFRa expression tends to be highest in the newly formed yolk sac regions. Namely, it is found first in the developing primitive endoderm (5.5-6.5 dpc) and subsequently in the periplacental yolk sac upon developing the chorioallantoic placenta and IPY (later than 11.5 dpc).