The activity of Ciona CiHox1 cis-elements in transgenic chicken embryos. A-B) Dorsal view of chicken embryos electroporated with 1UP1.4 construct with 1UP1.4 plus Hoxb1 expression constructs. 1UP1.4 activity is restricted to rhombomere 4 (A) and is expanded by Hoxb1 overexpression (B). C) As control, the mouse mb1 element is expressed in r4. D) Hoxb1 overexpression induces mb1 expanded activation in the whole hindbrain. E, F) Chicken embryos showing 1intro1.7 construct expression in the rhomboencephalon. F) 1intro1.7 activity is not influenced by Hoxb1 overexpression.