Fig. 8

Ntl/Bra Functions in an Autoregulatory Loop with Canonical Wnt Signaling

(A–H) Twenty-four hours postfertilization, embryos stained for myoD RNA expression from (A–G) the HS::dkk1-GFP line or (H) the ntl mutant. Temperature shifts (HS) were performed on hemizygous embryos at the indicated stage and then embryos were sorted based on GFP expression.

(B, C, and G) GFP⁺ embryos shifted at 75% epiboly phenocopy ntl/bra loss-of-function embryos.

(A–E) Lateral views; (F–H) dorsal views at the posterior end of the myoD-expressing region.

(I–L) Posterior view of four-somite (4s) HS::dkk1-GFP outcross embryos temperature shifted at 75% have a loss of (J) ntl and (L) bra expression in the mesodermal precursors of GFP⁺ embryos (arrowheads).

(M–P) Lateral view of HS::ΔTCF-GFP outcross embryos temperature shifted at the eight-somite stage and fixed 30 min afterward have a loss of (N) ntl and (P) bra expression in GFP⁺ embryos.

(Q) A schematic of a somitogenesis-stage embryo shown from a dorsal view with anterior to the top, illustrating two different functions of ntl and bra during mesoderm development. In the notochord (red), ntl and bra are involved in a putative autoregulatory loop with fgfs and are upstream of wnt11 and flh, whereas in the paraxial mesodermal precursors (green), ntl and bra function in an autoregulatory loop with canonical Wnts to maintain precursors throughout somitogenesis. Canonical Wnts also regulate the presomitic mesoderm.