Ten identified midline and tracheal enhancers.

1 The size of the minimal fragment with enhancer activity,
2 the position of the enhancer relative to the gene and 3midline and 4tracheal cells that exhibit enhancer activity are indicated.
3,4 The stage of development when reporter expression is first observed is indicated in parentheses. The absence of expression in the midline or trachea is indicated with a dash.