(A to C) Nuclear TCF clears from mesoderm
(brackets; SoxB1-negative; see fig. S9 for lineage identification using SoxB1) in control embryos.
(D to F) Without Notch or (G to
I) NLK, nuclear TCF persists in inner veg2
descendants (brackets). (J) Summary of endomesoderm segregation
steps. (Step 1) Notch inhibits the Hox11/13b regulatory circuit in
mesoderm (green box) by HB stage to initiate segregation. The Hox11/13b circuit
stays active in endoderm (yellow). (Step 2) Consequently, by MB
stage, Hox11/13b- and Brachyury-dependent expression of wnt1 is
restricted to endoderm, where it reinforces cWnt signaling and endoderm fate.
(Step 3) By pregastrula stage, a Notch-NLK pathway clears
nuclear TCF from mesoderm, making it unresponsive to cWnt. The endoderm retains
nuclear TCF and cWnt sensitivity.