The expression of Flrt3 during chick limb development.

The Flrt3 (Fibronectin-Leucine-Rich Transmembrane protein) gene encodes a fibronectin and leucine-rich repeat transmembrane protein whose expression is controlled by fibroblast growth factors (FGFs). FLRT3 has been implicated in neurite outgrowth after nerve damage, as a positive regulator of FGF signalling and in homotypic cell adhesion. Here we describe Flrt3 expression during chick embryonic limb development using whole-mount in situ hybridization. We found very dynamic expression during apical ridge formation and limb bud outgrowth. Initially Flrt3 is expressed in the apical ectodermal ridge and underlying mesenchyme, but then becomes restricted to the dorsal and ventral sides of the apical ridge as a twin stripe. At later stages, abundant expression is seen in the hindlimb and in both the pectoral and pelvic girdle-forming regions. FLRT3 may have a crucial role in regulating cellular adhesion between the epithelial apical ridge and the underlying mesenchyme and in establishing the dorso-ventral position of the ridge.