Re‐programming of expression of the KGFR and bek variants of fibroblast growth factor receptor 2 during limb regeneration in newts (Notophthalmus viridescens)

Abstract

We have previously shown, by in situ hybridization, that fibroblast growth factor receptor 2 (FGFRB) is present in the basal layer of wound epithelium during limb regeneration in newts (Notophthalmus viridescens). In contrast, FGFRl expression is observed throughout the blastema mesenchyme but is distinctly absent from the wound epithelium (Poulin et al. [1993] Development 1193534361). Sequence analysis revealed that we have isolated both the KGFR and bek variants of FGFR2. These two variants differ only in the second half of the last of their three (or two) Ig-like domains. In this report, we show the expression patterns of FGFRB variants during limb regeneration by in situ hybridization. During the pre-blastema stages of regeneration, FGFRB expression was observed in the basal layer of the wound epithelium and in the cells of the periosbum. The wound epithelial hybridization was observed when the KGFR-specific probe was used while the bek-specific probe hybridized to mRNA in the cells of the periosteum. As regeneration progresses to the blastema stages, KGFR expression continued to be observed in the basal layer of the wound epithelium with additional hybridization seen in the blastema mesenchyme closely associated with the bisected bones. The bek-specific hybridization pattern observed at this stage corresponds specifically to the mesenchymal hybridization. In the differentiation stages of regeneration, the mesenchymal expression of FGFR2 becomes restricted to the cells of the condensing cartilage and later to the perichondrium. Interestingly, there appears to be a dorsoventral gradient of the expression of both KGFR and bek variants of FGFR2, which are opposite each other at the later stages of regeneration. Thus, re-programming of expression of the two FGFR2 variants is required during the initial wound closure of limb regeneration. Remarkably, the expression patterns of KGFR and bek mimic those observed in the mouse limb bud during early embryonic development (Orr-Urtreger et al. [1993]

Changes in the expression of fibroblast growth factor receptors mark distinct stages of chondrogenesis in vitro and during chick limb skeletal patterning

“…In amphibians, fgfr 1, fgfr 3, and fgfr 4 transcripts are localized to the primordia of skeletal elements (Launay et al, 1994). In the regenerating newt limb, fgfr 2 mRNA is found first in condensing cartilage, then in the perichondrium (Poulin et al, 1993), similar to our observations in developing chick limbs. In a ten-day-old chick embryo (Patstone et al, 19931, fgfr 1, 2, and 3 mRNAs are localized to distinct regions of developing cartilage.…”

Mechanisms of urodele limb regeneration

“…Fgf1, Fgf2, Fgf8, and the anterior gradient protein (AG) are expressed by the AEC in vivo (Christensen, Weinstein, & Tassava, 2001, 2002; Han, An, & Kim, 2001; Kumar & Brockes, 2007). Blastema cells express the bek (FGFR2) receptor for Fgfs (Poulin & Chiu, 1995; Poulin, Patrie, Botelho, Tassava, & Chiu, 1993) and the AG receptor Prod1 (Kumar & Brockes, 2007). Fgf1 elevated the mitotic index of cultured blastema cells (Albert & Boilly, 1988; Albert, Boilly, Courty, & Barritault, 1987; Boilly, Cavanaugh, Hondermarck, Bryant, & Bradshaw, 1991), and Fgf2 elevated the mitotic index of blastema cells in amputated limbs covered by full‐thickness skin (Chew & Cameron, 1983).…”

Differential expression of myogenic regulatory genes and Msx‐1 during dedifferentiation and redifferentiation of regenerating amphibian limbs

“…FGF family members have recently been shown to be key signals during mouse and chick limb development necessary to maintain proliferation of the undifferentiated progress zone cells Fallon et al, 1994). The role of FGFs during regeneration has not been elucidated, however at least one member of the FGF family, aFGF, is present within the regenerating blastema (Boilly et al, 1991) and receptors for FGFs are expressed in both the ectoderm and throughout the mesenchyme of the blastema (Poulin et al, 1993). Thus FGFs are in a position to play a role in supporting blastema cell proliferation.…”