Effects of various growth factors (FGFs, IGF-1) on the limb buds of the slow-worm embryos (Anguis fragilis L.).

The present experiments were carried to investigate the effects of some gro wth factors (FGFs, IGF-1) on the development of limb buds in the slow-worm (Anguis fragilis L.). This serpentiform reptile is devoid of legs in adulth ood; but anlagen of limbs appear during embryonic life; their existence is only temporary: their growth ceases, they regress and disappear before hatc hing. Treatment of embryos was performed either by injection of the drugs a round the limb buds or by application of small fragments of cellulosic pape r soaked in the growth factors. The embryos were treated (27 by injection, 24 by application of cellulosic paper) at the stage of the allantoic bud 0. 2 mm to 0.5 mm long and at an older stage (allantoic bud 1.8 mm to 4 mm lon g) (21 embryos treated). The administered growth factors were FGF-2, FGF-4 and IGF-1. Dosages were around 1 000 to 3 900 ng. Anterior limb buds displa y only very weak sensitivity to the effect of the applied growth factors: o nly a small proportion of the treated embryos presented a weak hypertrophy of these buds; however, after application of a fragment of cellulosic paper soaked in FGF-2, two thickening of the somatopleure in a embryo and two sa lient buds in another developed in the territory of the limb, propably repr esenting anlagen of supernumerary limbs. In 25% of the embryos treated at t he stage of the allantoic bud 1.8 to 4 mm long, the anlagen of the posterio r limbs were greatly stimulated under the action of FGFs and IGF-I: the vol ume of the treated limbs was several times greater than the one of control limbs; histological study showed in the hypertrophied buds, numerous mitose s in the mesoblast and an apical ridge which did not degenerate. These resu lts are in agreement with previous experiments and they show that it is pos sible to check experimentally the evolutive regression of the limbs of Angu is embryos. (C) Elsevier, Paris.