Comparison of diverged Hoxc8 early enhancer activities reveals modification of regulatory interactions at conserved cis-acting elements.
The Hoxc8 early enhancer that controls the initiation and establishment of Hoxc8 expression in the developing mouse embryo is found in different vertebrate lineages including mammals, birds and fish. Mouse and Fugu Hoxc8 early enhancers (200 bp) have diverged in the composition of elements located towards the 3' region. However, they share cis-acting elements A-E located in the 5' region. Mutations at these elements in the context of the mouse Hoxc8 early enhancer affect reporter gene expression in the posterior neural tube, somites and lateral plate mesoderm of day 9.5 mouse embryos. Here, we demonstrate that mutations introduced at the same elements but in the context of the Fugu Hoxc8 early enhancer had different consequences on the reporter gene expression in transgenic mouse embryos. Furthermore, in contrast to the mouse enhancer the Fugu enhancer does not utilize elements D and E in achieving posterior neural tube and somite expression. These results suggest that the diverged sequences prevent regulatory interactions at conserved cis-acting elements. We propose that divergent sequences modify regulatory interactions at conserved elements by providing a "contextual change". Our finding that the enhancer elements do not act in a unitary fashion but function in the context of the surrounding sequence brings a new dimension to the study of cis-regulatory evolution.
Shashikant
Cooduvalli S
CS
Department of Dairy and Animal Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA 16802, USA. css13@psu.edu
Bolanowsky
Stacey A
SA
Anand
Sanjay
S
Anderson
Shawn M
SM
D000818:Animals; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004622:Embryo, Mammalian / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics* / Q000502:physiology; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter / Q000235:genetics; D014644:Genetic Variation; D018398:Homeodomain Proteins / Q000235:genetics*; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D054259:Neural Tube / Q000378:metabolism; D019170:Somites / Q000378:metabolism; D023741:Takifugu
D018398:Homeodomain Proteins; C489816:Hoxc8 protein, mouse