Figure 6.

 The distribution of Sim and Trh accessory factors. The HIF1α/ARNT pentamer reporter was used to follow the distribution of Sim or Trh accessory factors. (A) Following induction of Trh–Sim PAS (which we regard functionally as a Sim protein), ubiquitous expression of the reporter was observed (green). Arrowheads show the ventral borders of the tracheal pits. (B) The reporter is induced in all dorsal and dorsolateral ectodermal cells, after induction of Trh (borders shown by arrowheads). No expression was observed in the ventral ectoderm. Normal expression of the reporter in the midline (m) was also monitored. Red staining represents anti-Trh antibodies; these antibodies also recognize the Trh–Sim PAS chimera.