Fig. 4.

cis-Regulatory analysis of the hesC gene. (A) Expression pattern of the hesC GFP reporter reveals four domains at mesenchyme blastula stage: (1) low reporter activity in ectoderm outside of the apical plate and part of presumptive endoderm; (2) high activity in the preendoderm cells proximal to the NSM; (3) medium-low activity in NSM; and (4) no expression in the already ingressed SM cells (exposure time: 375 msec). The embryos were oriented identically and superimposed on them was the stenciled pattern shown in red. Quantitative data for embryos displaying each variant of the expression patterns in these experiments are given in Table 2. (B) Effect of disruption of Blimp1 binding site in intron 1 of the hesC locus. Strong expression of hesC reporter now occurs both in NSM (zone 3) and, unexpectedly, in SM (zone 4), demonstrating that Blimp1 is responsible for the persistent extinction of hesC transcription in both mesodermal territories (exposure time: 268 msec). (C) Effect of mutating Su(H) binding site in the hesC reporter. Activity is now lost in the zone 3 NSM, and greatly diminished activity in the endoderm of zone 2 (exposure time: 920 msec). (D) Subcircuit diagram showing Blimp1 repression input into both itself (18) and hesC (this work). (E) Subcircuit showing Delta-Notch signaling input (chevron) from neighboring cell into hesC gene and HesC repressive input back into delta.