RRC ID 50425
Author Fujiwara S, Cañestro C.
Title Reporter Analyses Reveal Redundant Enhancers that Confer Robustness on Cis-Regulatory Mechanisms.
Journal Adv Exp Med Biol
Abstract Reporter analyses of Hox1 and Brachyury (Bra) genes have revealed examples of redundant enhancers that provide regulatory robustness. Retinoic acid (RA) activates through an RA-response element the transcription of Hox1 in the nerve cord of the ascidian Ciona intestinalis. We also found a weak RA-independent neural enhancer within the second intron of Hox1. The Hox1 gene in the larvacean Oikopleura dioica is also expressed in the nerve cord. The O. dioica genome, however, does not contain the RA receptor-encoding gene, and the expression of Hox1 has become independent of RA. We have found that the upstream sequence of the O. dioica Hox1 was able to activate reporter gene expression in the nerve cord of the C. intestinalis embryo, suggesting that an RA-independent regulatory system in the nerve cord might be common in larvaceans and ascidians. This RA-independent redundant regulatory system may have facilitated the Oikopleura ancestor losing RA signaling without an apparent impact on Hox1 expression domains. On the other hand, vertebrate Bra is expressed in the ventral mesoderm and notochord, whereas its ascidian ortholog is exclusively expressed in the notochord. Fibroblast growth factor (FGF) induces Bra in the ventral mesoderm in vertebrates, whereas it induces Bra in the notochord in ascidians. Disruption of the FGF signal does not completely silence Bra expression in ascidians, suggesting that FGF-dependent and independent enhancers might comprise a redundant regulatory system in ascidians. The existence of redundant enhancers, therefore, provides regulatory robustness that may facilitate the acquisition of new expression domains.
Volume 1029
Pages 69-79
Published 2018-1-1
DOI 10.1007/978-981-10-7545-2_7
PMID 29542081
MeSH Animals Embryo, Nonmammalian / metabolism Embryo, Nonmammalian / ultrastructure Enhancer Elements, Genetic / drug effects Enhancer Elements, Genetic / genetics* Fetal Proteins / genetics Fetal Proteins / physiology Fibroblast Growth Factors / physiology Gene Expression Regulation, Developmental* / drug effects Gene Expression Regulation, Developmental* / genetics Genes, Reporter* Homeodomain Proteins / biosynthesis Homeodomain Proteins / genetics Mesoderm / metabolism Nerve Tissue Proteins / biosynthesis Nerve Tissue Proteins / genetics Nervous System / embryology Notochord / metabolism T-Box Domain Proteins / genetics T-Box Domain Proteins / physiology Tretinoin / physiology Urochordata / embryology Urochordata / genetics*
IF 2.45
Times Cited 1
Resource
C.intestinalis / (O.japonicus) Wild C. int