Fig. 3. Msx1 mediates the repression of Dbx2 by BMPs. (A,B) Dbx2 and Msx1 expression domains are juxtaposed. (A) Expression of Dbx2 and Msx1 in a stage 24 wild-type sample. Confocal microscopy reveals that cells do not co-express these proteins. (B) The mutually exclusive expression of these proteins is retained in samples expressing activated BMPR (viral infection, stage 24). Arrowhead indicates cells expressing Msx1 ventral to its normal expression border. Confocal microscopy reveals that these cells do not express Dbx2. (C-E) Mis-expression of Dbx2 does not affect Msx1 expression. Samples were generated by electroporation of viral DNA that drives Dbx2 expression and analyzed at stage 23. Brackets indicate a region of cells expressing Dbx2 within the normal Msx1 domain; bars represent endogenous Dbx2 expression domain. Virally infected cells express Dbx2 at levels equal to or higher than those in the endogenous domain. (C) Expression of Msx1 is unaltered by ectopic expression Dbx2. Co-expressing cells are apparent in D; E shows that many cells in the endogenous Msx1 domain are expressing Dbx2. (F,G) Mis-expression of Msx1 represses Dbx2 expression. Embryos were injected with an Msx1-expressing virus and analyzed at stage 24. Arrowhead denotes a region of ectopic Msx1 expression. (F) Gaps in the Dbx2 expression domain are apparent in the Msx1-infected samples. (G,H) These gaps correspond precisely with those cells that ectopically express Msx1.
