Fig. 8. Expression and mutant phenotype of noc. (A) noc RNA is first seen at stage 5 in the anterior region of the embryo. (B) At stage 6 a striped pattern is observed. (C) At stage 11, prominent expression is seen in the tracheal pits. (D) Expression is broad and uniform from stage 13. (E) Uniform tracheal expression of a noc EP2000 element does not give rise to tracheal phenotypes or the elimination of expression of the visceral enhancer trap marker l(2)01351 (arrow, green). (F) noc mutant embryos show tracheal defects that are similar to but weaker than the defects seen in elB mutants. Note the reduced lateral trunk anterior (arrow) and the shortened ganglionic branch (arrowhead). Tracheal nuclei are stained with anti-Trh (red). (G) In wild-type embryos, only the terminal cell of each dorsal branch expresses SRF (green, arrow). (H,I) In noc mutant embryos, the fusion cell also expressed SRF (arrows). This may account for the lack of dorsal trunk fusion in noc and elB mutants. It correlates with the specific late expression of ElB in the fusion cells, and implies a role for ElB/Noc in repressing expression of terminal cell markers in the fusion cell. (J) Fusion of lateral branches was also disrupted in noc mutants (arrows).

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