Mechanism of Fgf‐Mediated Lhx2 Upregulation

Abstract

IntroductionDuring development, fibroblast growth factors (FGFs) secreted from the apical ectodermal ridge (AER) direct limb outgrowth. FGFs also coordinate limb patterning through cross‐talk with other signaling molecules. The LIM homeobox transcription factor LHX2 is a suspected regulator of patterning cross‐talk, is expressed at the distal tip of the limb bud subjacent to the AER, and is a primary response target of FGF (Figure 1). However, the mechanism by which FGFs upregulate LHX2 is unknown. There are four major FGF signaling pathways through which regulation may occur: Jak/Stat, PLCγ, AKT, and Ras‐related (Figure 2). Based on the suspected roles of each signaling pathway, we hypothesize that FGF mediates LHX2 upregulation through the Ras‐related pathway.MethodsTo determine whether FGFs regulate LHX2 through the Ras‐related pathway, we injected the chemical inhibitor Salirasib (2.5 mM) into the anterior, posterior, and distal tips of the right limb of chick embryos at Hamburger‐Hamilton stage 21–22 (Figure 3). We also examined the potential function of the other Fgf pathways using pathway‐specific inhibitors. The embryos were harvested 24 hours after treatment and assessed for morphology. Whole mount in situ hybridization for LHX2 was then performed (Figure 4).ResultsPreliminary results indicate that inhibition of the Ras‐related pathway caused growth inhibition of the treated limbs in all embryos. In addition, LHX2 expression was markedly decreased in the these limbs. Treatment with a PLCγ‐specific inhibitor did not alter limb growth, while an AKT‐specific inhibitor impaired limb growth and LHX2 expression.ConclusionThese results suggest that the Ras‐related and AKT pathways control Fgf‐mediated LHX2 upregulation, whereas PLCγ does not. Further studies are needed to confirm these findings and to evaluate the Jak/Stat pathway.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.