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. 2022 Oct 17;377(1865):20210258. doi: 10.1098/rstb.2021.0258

Figure 3.

Figure 3.

Amniotic ectoderm establishment and expansion in the mouse. (a) (i) shows a lateral three-dimensional view of a reconstructed EHF stage embryo (EMA17, eMAP) [22] (only the amniotic, embryonic and extraembryonic ectoderm and the primitive streak are shown); (ii) shows a rotated and tilted dorsal view of the amniotic and embryonic ectoderm and the primitive streak. Descendants of the four clone types that contributed to amniotic ectoderm establish different regions of the amnion. The projection of the node and the ASP mark along the anteroposterior axis domain borders. (b) Initial injection position in epiblast of 12 clones that contribute to amniotic ectoderm (top) and final distribution of the respective clone descendants after amnion/chorion separation (bottom) at EHF. All clone types except type IV contribute only a minority of descendants to the amniotic ectoderm, the majority of their descendants passing through the primitive streak and into the extraembryonic mesoderm or remaining as surface ectoderm (type III) (not presented; see table 1 in [30]). (c) Inferred expansion of one representative of clone type I to IV, and one new type IV mixed clone that also contributed to surface ectoderm. Injected clones are indicated by arrows. The intermediate plotted positions in ES, LS and LSEB stages are speculative, but based on the expansion of epiblast from anterior to posterior [31], the final position of clone descendants at the EHF end stage, and clonal histories [30]. The rotated and tilted embryo shapes in (b,c) show only epiblast/embryonic ectoderm, primitive streak and amniotic ectoderm. Embryo shapes were derived from three-dimensional views of reconstructed embryos for PS, ES, MS, LS and LPHF/EHF stages (eMAP) [22] and interpolations for MS and LSEB/EPHF based on external measurements of intact embryos and measurements over the amnion in EMA 224 (LSEB/EPHF) (eMAP) [22]. The clones are from [30] (type 1: #1, type II: #15, type III: #18, type IV: #27) except for the type IV mixed clone that unlike other amniotic ectoderm restricted type IV clones also contributes to surface ectoderm (unpublished, K.A.L, see electronic supplementary material, table S1). ASP: anterior separation point; E: embryonic day; EHF: early headfold; ES: early streak; MS: midstreak; LS: late streak; LSEB: late streak, early allantoic bud; PS: prestreak.