Table 1.
Comparison of human and murine placentas.
| Feature | Euploid Human | T21 Human | Wild-type Murine | DS Mouse Models |
|---|---|---|---|---|
| Gross Shape | Discoid | Unchanged | Discoid | Unchanged |
| Transport Barrier | Hemochorial | Unchanged | Hemochorial | Unchanged |
| Trophoblast layers | Monochorial (1 STB layer) | Abnormal (2 layers due to defective cell fusion) | Trichorial (2 STB layers and 1 TGC layer) | Unknown |
| Site of Fetal-Maternal Exchange | Chorionic villi (via STB) | Abnormal (abnormal cell fusion and signaling) | Labyrinth (via STB) | Abnormal in T16 model |
| Syncytiotropho-blast Fusion | Syncytin 1 and 2 | Abnormal (delayed or absent) | Syncytin A and B | Unknown |
| Hormone synthesis | STB | Abnormal | TGC, SpTb | Unknown |
| Decidual/Endo-vascular Invasion | Extravillous trophoblast (interstitial and endovascular) | Abnormal (increased apoptosis, abnormal cell signaling and decreased invasion) | Primary TGC (implantation), Glycogen cells (only interstitial invasion), Secondary TGC (endovascular invasion) | Decreased glycogen and giant cells in T16 model |
| Endometrial Decidualization | Day 14 of menstrual cycle | Unchanged | Begins at fertilization | Unknown |
| Maternal uterine natural killer cells | Secretion of VEGF and NO to promote invasion | Unknown | Secretion of VEGF and NO to promote invasion | Unknown |
| Selective MHC class I expression by trophoblast | HLA-C, -G, E | Abnormal (Decreased expression of HLA-G) | H2–K | Increased expression in T16 model |
| Oxidative stress | Increases throughout gestation | Abnormally elevated | Increases throughout gestation | Unknown |
| Gestational length | 40 weeks | Unchanged | 3 weeks | Unchanged |
| Embryos | 1 | Unchanged | 4–12 | Decreased |
| Vascular invasion | Myometrial involvement (First 1/3) | Abnormal | Limited to the decidua | Unknown |
| Regulators of angiogenesis | VEGF, PlGF, sFlt-1 | Abnormal (Decreased levels of PlGF) | VEGF, Proliferin, sFlt-1 | Unknown |
| Placental Hormones | hGH/hCS 5-member gene cluster, Prolactin, Adipokines, hCG, Progesterone | Abnormal (Abnormal hCG production and secretion) | Prl 22-member gene cluster, growth hormone, placental lactogens, Progesterone, Adipokines | Unknown |
| Spiral arteries | 100–150 | Unknown | 5–30 | Unknown |
| Transformation of Spiral Arteries | Trophoblast dependent (with uterine natural killer cell assistance) | Abnormal | Uterine natural killer cell dependent | Unknown |
| Choriovitelline Placenta | Transient role in early pregnancy | Unchanged | Functions throughout pregnancy | Unchanged |
| Stem cell differentiation | Mediated by low oxygen tension | Abnormal (Increased oxidative stress) | Mediated by low oxygen tension | Unknown |
| Progesterone Production | Corpus luteum until, then STB | Defective | Corpus luteum throughout gestation | Unknown |
| Development of the choriovitelline placenta (yolk sac) | Day 8 | Unknown | Day 8 | Unknown |
| Early nutrition | Histiotrophic from endometrial glandular secretions | Unchanged | Histiotrophic from endometrial glandular secretions | Unchanged |
| Establishment of chorioallantoic circulation | 12 weeks | Unknown | Day 10.5 | Unknown |
| Temporal relationship | First trimester | Unchanged | Mid trimester | Unchanged |
TGC = Trophoblast giant cell, STB = syncytiotrophoblast, SpTb = spongiotrophoblast, VEGF = vascular endothelial growth factor, NO = nitric oxide, hGH = human growth factor, hCS = human chorionic sommatotropin, hCG = human chorionic gonadotropin Prl = prolactin, sFlt-1 = soluble fms-like tyrosine kinase.