Sm. Cannata et al., Nerve-independence of limb regeneration in larval Xenopus laevis is correlated to the level of fgf-2 mRNA expression in limb tissues, DEVELOP BIO, 231(2), 2001, pp. 436-446
In both larval and adult urodele amphibians, limb blastema formation requir
es the presence of an adequate nerve supply. In previous research, we demon
strated that the hindlimb of early Xenopus laevis larvae formed a regenerat
ion blastema even when denervated, while the denervated limb of late larvae
did not. We hypothesized that the nerve-independence was due to the autono
mous synthesis of a mitogenic neurotrophic-like factor by undifferentiated
limb bud cells. In this paper, we demonstrate that fgf-2 mRNA is present in
larval limb tissues and that its level is correlated to the extent of mese
nchymal cells populating the limb: in early limbs, fgf-2 mRNA is present at
high levels all over the limb, while, in late limbs, the fgf-2 expression
is low and detectable only in the distal autopodium. After denervation, fgf
-2 mRNA synthesis increases in amputated early limbs but not in amputated l
ate limbs. The implantation of anti-FGF-2 beads into amputated early limbs
hardly lowers the mitotic activity of blastema cells. However, FGF-2 beads
implanted into the blastema of late limbs prevent the denervation-induced i
nhibition of mitosis and oppose blastema regression. Our data indicate that
FGF-2 is a good candidate for the endogenous mitogenic factor responsible
for blastema formation and growth in amputated and denervated early limbs.
However, in amputated late limbs, the very limited fgf-2 expression is not
sufficient to promote blastema formation in the absence of nerves. (C) 2001
Academic Press.