Expression of FGF2 in the limb blastema of two Salamandridae correlates with their regenerative capability

Abstract

Limb regenerative potential in urodeles seems to vary among different species. We observed that Triturus vulgaris meridionalis regenerate their limbs significantly faster than T. carnifex, where a long gap between the time of amputation and blastema formation occurs, and tried to identify cellular and molecular events that may underlie these differences in regenerative capability. Whereas wound healing is comparable in the two species, formation of an apical epidermal cap (AEC), which is required for blastema outgrowth, is delayed for approximately three weeks in T. carnifex. Furthermore, fewer nerve fibres are present distally early after amputation, consistent with the late onset of blastemal cell proliferation observed in T. carnifex. We investigated whether different expression of putative blastema mitogens, such as FGF1 and FGF2, in these species may underlie differences in the progression of regeneration. We found that whereas FGF1 is detected in the epidermis throughout the regenerative process, FGF2 onset of expression in the wound epidermis of both species coincides with AEC formation and initiation of blastemal cell proliferation, which is delayed in T. carnifex, and declines thereafter. In vitro studies showed that FGF2 activates MCM3, a factor essential for DNA replication licensing activity, and can be produced by blastemal cells themselves, indicating an autocrine action. These results suggest that FGF2 plays a key role in the initiation of blastema growth.

Limb regeneration in higher vertebrates: Developing a roadmap

“…In addition, Fgf8 is also expressed in mesenchymal cells of the distal blastema in contrast to the AER-specific expression of Fgf8 in the limb bud (Han et al, 2001). FGF2 is immunolocalized to the AEC and the AER; however, during limb development FGF2 is also immunolocalized to the limb bud mesenchyme (Savage et al, 1993;Giampaoli et al, 2003). In regeneration, it is generally thought that Fgf1 and Fgf2 are transcribed in nerve cell bodies and transported to nerve terminals present in the AEC, where they are secreted (Mullen et al, 1996;Dungan et al, 2002).…”

“…The urodele AEC is known to express Fgf8 (Han et al, 2001;Christensen et al, 2002) and to accumulate FGF1 and FGF2 peptides (Mullen et al, 1996;Dungan et al, 2002;Giampaoli et al, 2003), but there are few functional studies that test the role of FGFs in regeneration. Details of the expression pattern of Fgf family members suggest that there are key differences between the AER of amniote limb buds and the AEC of urodele regenerating limbs.…”

De novo transcriptome sequencing of axolotl blastema for identification of differentially expressed genes during limb regeneration

“…Fibroblast growth factors (FGFs) participate in salamander limb regeneration [25-29]. For example, fgf - 8 is expressed in the basal layer of the apical epithelial cap [30].…”

Looking proximally and distally: 100 years of limb regeneration and beyond

“…Factors other than AGP that promote blastema cell proliferation in vitro have been detected in the wound epidermis of the regenerating limb, including Fgf-1, 2, and 8 (Chew and Cameron, 1983;Boilly et al, 1991;Zenjari et al, 1997;Han et al, 2001;Christensen et al, 2001Christensen et al, , 2002Dungan et al, 2002;Giampaoli et al, 2003). Likewise, nerves produce other mitogens including transferrin, Fgf-2, Ggf-2 (neuregulin), and substance P (Munaim and Mescher, 1986;Mescher and Kiffmeyer, 1992;Mescher et al, 1997;Globus and Alles, 1990;Anand et al, 1987;Mullen et al, 1996;Wang et al, 2000).…”