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Co‐Incident Upregulation of Shh and Hoxa 13 by Fgf in The Developing Limb Bud
Author(s) -
Real Daniel,
Watson Billy A,
Feenstra Jennifer M,
Pira Charmaine U,
Oberg Kerby C
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1032.3
Subject(s) - zone of polarizing activity , limb bud , apical ectodermal ridge , limb development , sonic hedgehog , fibroblast growth factor , mesoderm , fgf8 , microbiology and biotechnology , anatomy , biology , ectoderm , embryo , embryogenesis , embryonic stem cell , gene , genetics , signal transduction , receptor
Sonic hedgehog (Shh) is secreted from the zone of polarizing activity (ZPA) within the distal‐posterior limb bud mesoderm and regulates pattern and proliferation along the anterior‐posterior limb axis. Fibroblast growth factor 8 (Fgf8) is expressed in the distal limb bud from a rope‐like thickening called the apical ectodermal ridge (AER) and regulates proximal‐distal outgrowth and patterning. Once established, Shh and Fgf8 maintain each other's expression via a reciprocal loop, tightly regulating progressive limb development. Intermediates between Fgf and Shh are still being characterized. Gene arrays following application of Fgf2 to the posterior margin of developing chick wings showed up‐regulation of not only Shh, but also Hoxa13. Hoxa13 expression is a marker of the developing autopod or handplate. In the absence of Hoxa13, there is increased anterior apoptosis and disruption of the normal anterior‐posterior patterning. We hypothesized that the upregulation of Hoxa13 by Fgf in the posterior margin of the limb bud is important for the up‐regulation of Shh. To test this hypothesis Fgf2 or PBS soaked beads were implanted in the posterior limb margin of stage 23 chick wing buds. Embryos were harvested 24 hours after bead implantation for Hoxa13 whole mount in‐situ hybridization (WMISH). The results showed that Fgf induced ectopic Hoxa13 expression 24 hours after bead implantation. This confirmed the gene array data that showed a 13 fold increase in Hoxa13 following Fgf2 application. Limb‐specific Shh expression is regulated by the ZPA regulatory sequence (ZRS) which contains Hox binding sites important for full regulatory activity. Future studies are needed to establish whether Hoxa13 binding to the ZRS can facilitate Shh up‐regulation.