Table 1 Mutations affecting amnion formation

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]