EXPRESSION OF THE HEPATOCYTE GROWTH-FACTOR GENE DURING CHICK LIMB DEVELOPMENT

It has been shown that mirror-image duplications of the zeugopodia and digits are formed when MRC-B fibroblasts producing hepatocyte growth factor (HGF) are applied to the anterior region of the chick limb bud (Yonei et al, [1993] Dev. Biol. 160:246-253). To evaluate the role of HGF in limb development, we observed the expression pattern of the HGF gene using in situ hybridization. The HGF gene was expressed in the m esoderm of the limb bud and in the central core region of mandibular a rch and maxillary processes at stages 17 to 24. When both wing and leg buds begin to extend distally, the HGF gene is expressed in the mesen chymal cells, but not in the ectodermal cells and somites. Concomitant with establishment of the apical ectodermal ridge, distal mesenchymal cells of the limb bud express the HGF gene intensely with a gradient higher in the distal region, The HGF expression is later confined to t he ventral and subapical mesenchyme of the limb bud, although no signa l is detectable in the apical and non-ridge ectoderm. However, signal for the c-met proto-oncogene encoding the HGF receptor is not detectab le in the limb bud at stages 17 to 24. These results suggest that HGF produced in the limb mesoderm may be involved in initial induction and maintenance of the apical ectoderm during limb development. (C) 1995 Wiley-Liss, Inc.