Fig. 3. Identification and evolutionary conservation of three Krox20 regulatory elements. (A) Homology plots between chick fragments 7, 12 and 14 and corresponding mouse sequences generated using the VISTA algorithm. The horizontal axis represents the chick sequences with a scale in kilobases and the vertical axis the percentage of homology between mouse and chick sequences in a window of 100 bp with a resolution of 7 bp. Only homology superior to 50% is shown. Genomic chick fragments containing the five conserved elements (A, 12.1, B, 12.3 and C) and indicated by the above bars were cloned upstream of the ß-globin promoter-lacZ reporter. Each construct was tested by in ovo electroporation and transgenesis in the mouse as indicated in Fig. 2. (B) The table indicates the construct names, the presence (+) or absence (–) of activity in r3 and/or r5 in electroporated chick embryos (in ovo), the number of E8.5 transgenic embryos analysed (n) and the number of transgenic embryos expressing in r3 and r5 (r3/r5), the r3 to r5 region (r3-r5) or r5 only (r5). (C-H) Transgenic mouse embryos (C-E) and electroporated chick embryos (F-H), for the indicated constructs. r, rhombomere; ov, otic vesicle.