Abstract
Anterior–posterior (A–P) polarity of mouse embryos is established by distal visceral endoderm (DVE) at embryonic day (E) 5.5. Lefty1 is expressed first at E3.5 in a subset of epiblast progenitor cells (L1epi cells) and then in a subset of primitive endoderm cells (L1dve cells) fated to become DVE. Here we studied how prospective DVE cells are selected. Lefty1 expression in L1epi and L1dve cells depends on Nodal signaling. A cell that experiences the highest level of Nodal signaling begins to express Lefty1 and becomes an L1epi cell. Deletion of Lefty1 alone or together with Lefty2 increased the number of prospective DVE cells. Ablation of L1epi or L1dve cells triggered Lefty1 expression in a subset of remaining cells. Our results suggest that selection of prospective DVE cells is both random and regulated, and that a fixed prepattern for the A–P axis does not exist before the blastocyst stage.
Highlights
Anterior–posterior (A–P) polarity of mouse embryos is established by distal visceral endoderm (DVE) at embryonic day (E) 5.5
We have previously shown that Lefty[1] is expressed first in a subset of epiblast progenitor cells and in a subset of primitive endoderm (PrE) progenitors fated to become DVE8, with these Lefty1+ cell subsets being designated L1epi cells and L1dve cells, respectively
Some DVE cells were previously reported to be derived from epiblast (Sox2+ cells) that transmigrates into VE12
Summary
Anterior–posterior (A–P) polarity of mouse embryos is established by distal visceral endoderm (DVE) at embryonic day (E) 5.5. Our results suggest that selection of prospective DVE cells is both random and regulated, and that a fixed prepattern for the A–P axis does not exist before the blastocyst stage. A–P polarity is established in the mouse embryo when the distal visceral endoderm (DVE) migrates toward the future anterior side at embryonic day (E) 5.5 Type II embryonic region undergo global movement, resulting in the localization of some VE cells at the distal tip of the embryo These VE cells at the distal tip will become the anterior visceral endoderm (AVE) and migrate toward the future anterior side of the embryo by following the migration of DVE8. Our results suggest that selection of prospective DVE cells in mouse peri-implantation embryo is both random and regulated
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