An ultraconserved Hox-Pbx responsive element resides in the coding sequence of Hoxa2 and is active in rhombomere 4.
The Hoxa2 gene has a fundamental role in vertebrate craniofacial and hindbrain patterning. Segmental control of Hoxa2 expression is crucial to its function and several studies have highlighted transcriptional regulatory elements governing its activity in distinct rhombomeres. Here, we identify a putative Hox-Pbx responsive cis-regulatory sequence, which resides in the coding sequence of Hoxa2 and is an important component of Hoxa2 regulation in rhombomere (r) 4. By using cell transfection and chromatin immunoprecipitation (ChIP) assays, we show that this regulatory sequence is responsive to paralogue group 1 and 2 Hox proteins and to their Pbx co-factors. Importantly, we also show that the Hox-Pbx element cooperates with a previously reported Hoxa2 r4 intronic enhancer and that its integrity is required to drive specific reporter gene expression in r4 upon electroporation in the chick embryo hindbrain. Thus, both intronic as well as exonic regulatory sequences are involved in Hoxa2 segmental regulation in the developing r4. Finally, we found that the Hox-Pbx exonic element is embedded in a larger 205-bp long ultraconserved genomic element (UCE) shared by all vertebrate genomes. In this respect, our data further support the idea that extreme conservation of UCE sequences may be the result of multiple superposed functional and evolutionary constraints.
Lampe
Xavier
X
Unit of Developmental Genetics, Université Catholique de Louvain, 1200 Brussels, Belgium, Institut de Génétique et de Biologie Moléculaire et Cellulaire, UMR 7104 CNRS/INSERM/ULP, Collège de France, BP 10142-CU de Strasbourg, 67404 Illkirch Cedex, France.
Samad
Omar Abdel
OA
Guiguen
Allan
A
Matis
Christelle
C
Remacle
Sophie
S
Picard
Jacques J
JJ
Rijli
Filippo M
FM
Rezsohazy
René
R
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002642:Chick Embryo; D017124:Conserved Sequence; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D020218:Response Elements; D012249:Rhombencephalon / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation
D018398:Homeodomain Proteins; C489833:Hoxa2 protein, mouse; D014157:Transcription Factors