title: Manipulations of PKA in chick limb development reveal roles in digit patterning including a positive role in Sonic Hedgehog signaling.
abstract: Sonic Hedgehog (Shh) signaling by the polarizing region, at the posterior of the vertebrate limb bud, is pivotal in determining digit number and identity. Shh establishes a gradient of the bifunctional transcriptional effector, Gli3, with high levels of full-length activator (Gli3A) in the posterior bud, where digits form, and high levels of shorter repressor (Gli3R) in the anterior. Repressor formation depends on protein kinase A (PKA), but in Drosophila, PKA also plays a role in activator function. Increasing PKA levels in chick limb development using Forskolin had no effect on posterior polarizing activity but weak polarizing activity, based on ligand-independent Shh signaling, was induced in anterior limb bud cells resulting in extra digits. Manipulating PKA activity levels directly with a retrovirus expressing activated PKA induced extra digits similar to those induced by Forskolin treatment suggesting that PKA may have a previously unrecognized positive role in Shh signaling in vertebrate limbs. Expressing dominant negative PKA also induced extra, sometimes multiple digits, from anterior limb bud demonstrating the negative role in Shh signaling. PKA levels in the limb bud are high posteriorly and low anteriorly, suggesting that PKA activity may influence the outcome of Shh signaling in normal development.
authors: Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK. c.a.tickle@dundee.ac.uk
authors: Eva
authors: E
authors: Tiecke
authors: Roisin
authors: R
authors: Turner
authors: Juan Jose
authors: JJ
authors: Sanz-Ezquerro
authors: Anne
authors: A
authors: Warner
authors: Cheryll
authors: C
authors: Tickle
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019521:Body Patterning / Q000502:physiology*; D002642:Chick Embryo; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017931:DNA Primers; D005552:Forelimb / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology*; D053823:Hedgehog Proteins / Q000378:metabolism*; D017403:In Situ Hybridization; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D017931:DNA Primers; D053823:Hedgehog Proteins; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases