Upon gastrulation, the mammalian conceptus transforms rapidly from a simple bilayer into a multi-layered embryo enveloped by its extraembryonic membranes. Impaired development of the amnion, the innermost membrane, causes major malformations. To clarify the origin of the mouse amnion, we used single cell-labelling and clonal analysis. We identified four clone types with distinct clonal growth patterns in amniotic ectoderm (AmEc). Two main types have progenitors in extreme proximal-anterior epiblast. Early descendants initiate and expand AmEc posteriorly, while descendants of cells remaining anteriorly later expand AmEc from its anterior side. Amniogenesis is abnormal in embryos deficient in the BMP signalling effector SMAD5, with delayed closure of the proamniotic canal, and aberrant amnion and folding morphogenesis. Transcriptomics of individual Smad5 mutant amnions isolated before visible malformations, and tetraploid chimera analysis, revealed two amnion defect sets. We attribute them to impairment of progenitors of the two main cell populations in AmEc and to compromised cuboidal-to-squamous transition of anterior AmEc. In both cases, SMAD5 is critical for expanding AmEc rapidly into a stretchable squamous sheet to accommodate exocoelom expansion, axial growth and folding morphogenesis.
Amniotic ectoderm expansion occurs via distinct modes and requires SMAD5-mediated signalling
Contributed equally to this work
Present address: Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, United Kingdom
Lead contact: An Zwijsen
Currently Viewing Accepted Manuscript - Newer Version Available
Mariya P. Dobreva, Vanesa Abon Escalona, Kirstie A. Lawson, Marina N. Sanchez, Ljuba C. Ponomarev, Paulo N. G. Pereira, Agata Stryjewska, Nathan Criem, Danny Huylebroeck, Susana M. Chuva de Sousa Lopes, Stein Aerts, An Zwijsen; Amniotic ectoderm expansion occurs via distinct modes and requires SMAD5-mediated signalling. Development 2018; dev.157222. doi: https://doi.org/10.1242/dev.157222
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