Irx1 and Irx2 are coordinately expressed and regulated by retinoic acid, TGFβ and FGF signaling during chick hindlimb development

PLoS One. 2013;8(3):e58549. doi: 10.1371/journal.pone.0058549. Epub 2013 Mar 11.

Abstract

The Iroquois homeobox (Irx) genes play a crucial role in the regionalization and patterning of tissues and organs during metazoan development. The Irx1 and Irx2 gene expression pattern during hindlimb development has been investigated in different species, but its regulation during hindlimb morphogenesis has not been explored yet. The aim of this study was to evaluate the gene expression pattern of Irx1 and Irx2 as well as their regulation by important regulators of hindlimb development such as retinoic acid (RA), transforming growth factor β (TGFβ) and fibroblast growth factor (FGF) signaling during chick hindlimb development. Irx1 and Irx2 were coordinately expressed in the interdigital tissue, digital primordia, joints and in the boundary between cartilage and non-cartilage tissue. Down-regulation of Irx1 and Irx2 expression at the interdigital tissue coincided with the onset of cell death. RA was found to down-regulate their expression by a bone morphogenetic protein-independent mechanism before any evidence of cell death. Furthermore, TGFβ protein regulated Irx1 and Irx2 in a stage-dependent manner at the interdigital tissue, it inhibited their expression when it was administered to the interdigital tissue at developing stages before their normal down-regulation. TGFβ administered to the interdigital tissue at developing stages after normal down-regulation of Irx1 and Irx2 evidenced that expression of these genes marked the boundary between cartilage tissue and non-cartilage tissue. It was also found that at early stages of hindlimb development FGF signaling inhibited the expression of Irx2. In conclusion, the present study demonstrates that Irx1 and Irx2 are coordinately expressed and regulated during chick embryo hindlimb development as occurs in other species of vertebrates supporting the notion that the genomic architecture of Irx clusters is conserved in vertebrates.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone Morphogenetic Proteins / metabolism
  • Cell Death / genetics
  • Chick Embryo
  • Chondrogenesis / drug effects
  • Chondrogenesis / genetics
  • Fibroblast Growth Factors / pharmacology*
  • Gene Expression Regulation, Developmental / drug effects*
  • Hindlimb / embryology*
  • Homeodomain Proteins / genetics*
  • Signal Transduction*
  • Transcription Factors / genetics
  • Transforming Growth Factor beta / pharmacology*
  • Tretinoin / pharmacology*

Substances

  • Bone Morphogenetic Proteins
  • Homeodomain Proteins
  • Transcription Factors
  • Transforming Growth Factor beta
  • Tretinoin
  • Fibroblast Growth Factors

Grants and funding

This work was partially supported by grants 168642, 53484, 42568-Q, 34334-N from CONACyT, and by grants IN220808, IN200205, IX200410, IN214511 from DGAPA, UNAM. MEDH was the recipient of a scholarship from CONACYT, UNAM. MEDH and CIGH were the recipient of a scholarship from Red de desarrollo de fármacos y métodos de diagnóstico (FARMED). DGAPA, UNAM IN214511, IX200410, CONACYT 168842. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.