Fig. 5. Expression of a dominant-negative BMP receptor in lateral mesoderm results in enhanced expression of early hemato-vascular markers. (A-C) Representative embryos analyzed by in situ hybridization for expression of gata1. Views are flat-mounted dorsal, anterior towards the top. (A) Control uninjected embryo (B) Embryo that had been injected with I(lmo2:BR)I. (C) Embryo that had been injected with I(lmo2:cre)I. gata1 expression is markedly increased in lateral mesoderm both laterally (arrowheads) and in the caudal region of the embryos expressing BR, compared with the controls (arrow). (D-G) Representative embryos analyzed for myeloid markers. Views are ventral, anterior towards the top (D,E) or lateral, anterior towards the left (F,G). Compared with uninjected control embryos (D,F), the embryos transgenic for I(lmo2:BR)I (E,G) have increased expression levels of transcripts for l-plastin (E) and mpo (G) (arrowheads). (H) Control and (I) a corresponding representative I(lmo2:BR)I transgenic embryo analyzed for expression of the endothelial marker flk1. The embryos expressing the mutant receptor show enhanced levels of flk1 in the posterior tail (arrowheads). Views are lateral to the tail region, anterior towards the left. (J,K) Representative embryos from the fli:gfp transgenic line used to evaluate vascular development. Compared with control embryos (J), embryos expressing the mutant receptor in lateral mesoderm display dilation of the vasculature in the ICM region (arrowheads). Views are lateral, anterior towards the left.