Figure 8

BMP regulates the vascular-promoting factors and communicates with Notch. (A-D) Ectopic noggin expression in the lateral plate mesoderm (LPM, left panels) silences expression of Id2 (A, N = 3), Id3 (B, N = 3), FoxC2 (C, N = 4) and Snail1 (D, N = 2) in the lateral DM (arrows) compared to the contralateral sides (arrowheads). (E-H) Dorsal view of whole-mount segments. (E) Basal activity of Hes1 reporter in the lateral DM (N = 5). (F) Ectopic BMP expression enhances Hes1 reporter activity (N = 6). (G) Basal activity of the BMP reporter (N = 3). (H) aNotch2 induces BMP reporter activity (N = 7). (E’-H’) Control RFP shows similar electroporation efficiency in all treatments. (I) A gene regulatory network underlying lineage segregation in the lateral DM. BMP from the LPM positively regulates Notch activity and vice-versa. Notch/BMP signaling upregulate/maintain expression of Id2/3 and FoxC2 which, in turn, promote lateral DM cells to delaminate, migrate and differentiate into SM in blood vessels (BV) at the expense of skeletal muscle, partly by inhibiting Myf5 and Pax7 activities. Furthermore, Notch-dependent cellular EMT is mediated by Snail1 and Pax7 inhibits Notch signaling and Snail1 transcription. In addition, Id2/3 enhance Notch signaling and vice-versa and Id2/3 upregulate FoxC2 mRNA, altogether reinforcing the network. Bar: (A-D) 100 μm. BMP, bone morphogenetic protein; DM, dermomyotome; EMT, epithelial-to-mesenchymal transition; EP, electroporation; ISH, in situ hybridization; LPM, lateral plate mesoderm; M, myotome; RFP, red fluorescent protein; SM, smooth muscle.