Hemochorial placentation: development, function, and adaptations

Abstract

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

Figure 1.

Schematic representations of hemochorial placentation sites showing homologous structures within human, rat, and mouse. Note human and rat exhibit deep intrauterine trophoblast invasion, whereas trophoblast invasion in the mouse is shallow. (adapted from Ref. 241)

Figure 2.

Timeline of selected technical advancements in placental research. In vitro and in vivo approaches that have positively impacted placental research over the past 50 years are presented.

Figure 3.

Lentiviral-mediated trophectoderm gene delivery. (a) Procedure for lentiviral-mediated gene delivery. (b–d) Ubiquitin C promoter driven enhanced green fluorescent protein (EGFP) trophectoderm lentiviral delivery, transfer to pseudopregnant rats, and assessment at gestation day 13.5. Fetal–placental tissues were examined under bright field (b), fluorescence microscopy (c), or a merge of panels b and c (d). Note the placental-specific expression of EGFP. Scale bar = 2 mm (adapted from Ref. 163).

Figure 4.

Placentation site plasticity: responses to hypoxia exposure during rat pregnancy. (a) Chicken beta actin promoter-enhanced green fluorescent protein (chβA-EGFP) transgenic model for monitoring intrauterine trophoblast cell invasion. (b) Gestation day 13.5 placentation site from a rat exposed to ambient oxygen. (c) Gestation day 13.5 placentation site from a rat exposed to hypoxia (∼11% oxygen) from gestation day 6.5–13.5. Maternal hypoxia activated endovascular trophoblast invasion. Scale bar = 0.5 mm (adapted from Ref. 235).