Table 1.
Mutations affecting amnion formation
| Gene | Gene Product | Phenotype | Onset Phenotype | Lethality | Reference |
|---|---|---|---|---|---|
| Amn | Type I transmembrane protein | Amnion absent while extraembryonic structures like chorion, yolk sac blood islands, and allantois develop normally | E 6.5 - Prestreak, no amniotic fold | E 9.5 | [33,48,49] |
| Bmp1/Procollagen C-proteinase | Growth factor/protease | Amnion present but lacks the fold covering the loops of the gut in the umbilical ring region | E 11.5 | Perinatal | [6] |
| Bmp2 | Growth factor | Amnion has a delayed fusion or fails to fuse; heart is formed within the exocoelomic cavity as a result of lack of amnion fusion | E 7.0 - Late streak, large exocoelomic cavity | E8.5 to E9.5 | [34] |
| Ds (Ds mutation) | Not known | Semidominant mutation associated with early amnion rupture or amniotic band sequence (ABS) | E 18.5 | Viable | [58,59] |
| Evi1 | Transcription factor with zinc finger motifs | Amnion filled with fluid; unbalanced amniotic ectoderm and mesoderm | E 7.5 - Neural plate, amnion and chorion segregated | E10.5 | [60] |
| Fibronectin | High molecular-weight glycoprotein | Undersized amnion; amniotic cavity with pressure deficit | E 7.5 - Neural plate, amnion and chorion segregated | E9.5 to E10.5 | [4] |
| FoxF1 | Winged helix transcription Factor |
Undersized amnion tightens and restricts embryo growth; ectopic VCAM and receptor α1-integrin expression in amniotic mesoderm | E 7.5 - Neural plate, amnion and chorion segregated | E9.5 to E10.5 | [44] |
| Ldb1 | LIM domain-binding protein | Undersized amnion leading to constricted embryonic-extraembryonic junction | E 7.5 - Neural plate, amnion and chorion segregated | E9.5 to E10 | [61] |
| Paxillin | Focal adhesion molecule | Undersized amnion; amniotic cavity with pressure deficit | E 7.5 - Neural plate, amnion and chorion segregated | E8.5 to E9 | [62] |
| Smad5 | Bmp signaling intermediate | Delayed fusion of the amnion; Thickenings containing ectopic haematopoietic, endothelial and PGC-like cells | E 7.0 - Late streak/early bud, amnion fusion | E9.5 to E10.5 | [31,32,50] |
| *Flk1 | VEGF Receptor | In chimeras, Flk1 null cells fail to form blood islands and accumulate in amnion | E 7.5 - Neural plate, chorion and ectoplacental cone fuse | E9.5 | [63] |
| *Gastrulation mutants | not applicable | No mesoderm and amniochorionic fold forms, and consequently no amnion | E 6.5 - Prestreak, no amniotic fold | E7.5 | [64] |
* The observed amnion defects are considered secondary.