Human intronic enhancers control distinct sub-domains of Gli3 expression during mouse CNS and limb development.
BACKGROUND
The zinc-finger transcription factor GLI3 is an important mediator of Sonic hedgehog signaling and crucial for patterning of many aspects of the vertebrate body plan. In vertebrates, the mechanism of SHH signal transduction and its action on target genes by means of activating or repressing forms of GLI3 have been studied most extensively during limb development and the specification of the central nervous system. From these studies it has emerged, that Gli3 expression must be subject to a tight spatiotemporal regulation. However, the genetic mechanisms and the cis-acting elements controlling the expression of Gli3 remained largely unknown.


RESULTS
Here, we demonstrate in chicken and mouse transgenic embryos that human GLI3-intronic conserved non-coding sequence elements (CNEs) autonomously control individual aspects of Gli3 expression. Their combined action shows many aspects of a Gli3-specific pattern of transcriptional activity. In the mouse limb bud, different CNEs enhance Gli3-specific expression in evolutionary ancient stylopod and zeugopod versus modern skeletal structures of the autopod. Limb bud specificity is also found in chicken but had not been detected in zebrafish embryos. Three of these elements govern central nervous system specific gene expression during mouse embryogenesis, each targeting a subset of endogenous Gli3 transcription sites. Even though fish, birds, and mammals share an ancient repertoire of gene regulatory elements within Gli3, the functions of individual enhancers from this catalog have diverged significantly. During evolution, ancient broad-range regulatory elements within Gli3 attained higher specificity, critical for patterning of more specialized structures, by abolishing the potential for redundant expression control.


CONCLUSIONS
These results not only demonstrate the high level of complexity in the genetic mechanisms controlling Gli3 expression, but also reveal the evolutionary significance of cis-acting regulatory networks of early developmental regulators in vertebrates.
Abbasi
Amir A
AA
Department of Human Genetics, Philipps-Universität Marburg, 35037 Marburg, Germany. abbasiam@qau.edu.pk
Paparidis
Zissis
Z
Malik
Sajid
S
Bangs
Fiona
F
Schmidt
Ansgar
A
Koch
Sabine
S
Lopez-Rios
Javier
J
Grzeschik
Karl-Heinz
KH
D000818:Animals; D030801:Animals, Genetically Modified; D002490:Central Nervous System / Q000196:embryology*; D002642:Chick Embryo; D004742:Enhancer Elements, Genetic; D005121:Extremities / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics*; D000074290:Zinc Finger Protein Gli3
C065683:GLI3 protein, human; D051741:Kruppel-Like Transcription Factors; D009419:Nerve Tissue Proteins; D000074290:Zinc Finger Protein Gli3