Figure 5

Chorioallantoic placenta of the capybara at the limb bud stage I. (A) An extensive pad of spongy trophoblast is covered on the fetal surface by allantoic mesoderm. Note the cytotrophoblasts that occur at the surface and along the margins of the fold (arrows). Haematoxylin and eosin. (B) Immunostaining for cytokeratin is more intense in the cytotrophoblasts lining the fold than in the rest of the trophoblast pad. (C) Immunostaining for vimentin confirms the presence of fetal vessels within a fold. (D) Immunostaining for smooth muscle α-actin reveals that fetal vessels are beginning to ramify into the trophoblast at the margin of a fold. Cyt = cytotrophoblasts, fm = allantoic or fetal mesoderm, fv = fetal vessel, pad = trophoblast pad. Scale bars = 500 μm (A), 100 μm (B-C), 200 μm (D).