In these Pdgfraph/Pdgfraph mutants, macroscopically the placental disc, the yolk sac, and the vascular connections between the fetus and these organs appeared normal, except that the placental disc was smaller than those of normal littermates and the villous portion of the visceral yolk sac seemed to be less developed with fewer and shorter villi (Fig. 5B). However, as shown in Figure 4, С and G, histological studies revealed that no IPY was formed in the placental discs of the Pdgfraph/Pdgfraph mutants, while the structure of the other components—junctional zone, labyrinthine layer, and chorion—seemed to form normally. Although the parietal endoderm and the junctional zone expressed PDGFRot, PDGFRa may not be essential to the development of these structures at least in these Pdgfraph/ Pdgfraph mutants.
To examine the expression of calbindin-D9k mRNA in the placental disc of Pdgfraph/Pdgfraph mutants, ISH for calbindin-D9k was performed on 14.5- and 17.5-dpc Pdgfraph/Pdgfraph placentas. As shown in Figure 4, D and H, in Pdgfraph/Pdgfraph placentas strong signals were detected in the epithelial cells at the border of parietal and visceral endoderms, and weak signals were detected in the villous visceral endoderm. No signals were detected in the placental disc. asthma inhalers
The Pdgfraph mutation exhibits not only recessive phenotypes but also a dominant phenotype, white spotting. This coat color phenotype is surmised to be a result of the altered expression of the с-kit gene, which is located next to the Pdgfra gene on a normal chromosome and is intact in the Pdgfraph mutation . Therefore, we examined whether the aberrant expression of c-kit was present in the Pdgfraph/Pdgfraph placenta. Immunostaining with anti-c-kit antibody, ACK2, showed that it was expressed in the decidual and labyrinthine layers in normal placentas (Fig. 5A), as previously reported , and no ectopic expression of it was present in Pdgfraph/Pdgfraph placenta (Fig. 5B). This observation indicates that the absence of the IPY in Pdgfraph/Pdgfraph mutants is a direct outcome of the loss of PDGFRot.
FIG. 5. Expression of c-kit in the wild-type and Pdgfraph/Pdgfraph placenta. A) A placenta of a wild-type 15.5-dpc embryo was immunostained with ACK2. The expression of c-kit in the labyrinthine (I) and decidual layer (d) was detected. B) A placenta of a T 5.5-dpc Pdgfran/Pdgfraph embryo derived from the BD-Pdgfraph colony was immunostained with ACK2. No ectopic c-/«f-expression was detected, j, junctional zone.