[Effects of cytosine-arabinofuranoside on the development of reptilian embryos (Lacerta viridis, Laur. and Anguis fragilis, L.)].

Abstract

Administered into the yolk sac of eggs of Lacerta viridis as a single dose of 17 to 40 micrograms, cytosine-arabinoside (Ara-C) was compatible with survival of the embryo, from the sixth day of incubation, for at least 20 to 25 days. The LD50 was 40 to 50 micrograms per egg. Doses of 20 to 40 micrograms of Ara-C introduced in the yolk sac of eggs of the slow-worm (Anguis fragilis) cultured in vitro, at stages of the allantoid bud of 0,5 mm to 2,5 mm long, killed the embryo in 4 to 8 days (possibly due to alterations of capillary blood vessels of allantois and area vasculosa). In the two species, these doses caused cytotoxic effects on embryonic proliferating tissues, growth inhibition and a variety of developmental defects. In young embryos of Anguis fragilis, similar doses of 20 to 40 micrograms of Ara-C caused, in 2 to 4 days, death of many cells in the anlagen of growing organs: neural tube, sensory organs, bronchi, mesoderm of the limb bud, subcutaneous mesenchyme, anlage of dorsal skeletal structures, etc.; followed by growth inhibition and malformations. On the other hand, in the limb bud, the apical ridge was less retrogressed than in control embryos; the limb buds showed slightly better development in treated embryos than in controls, but, Ara-C induced severe damage in their mesoderm. In all embryos of Lacerta viridis, treated at the stage of 6 days or of 10 days of incubation by doses of 20 to 40 micrograms of Ara-C and killed 15 to 35 days later, there was a general reduction of size and of weight and external and internal malformations, more or less severe, were present: modifications of the form of the head, shortening of the lower jaw, labial clefts, microphthalmia, micromelia and other limbs defects, developmental defects of the tail. In some embryos, the only external defects observed were missing fingers and toes; in three of these embryos, the same digits were missing in the four limbs. Modifications of limb morphogenesis induced by Ara-C are compared to structural modifications of the limbs of snake-like Reptilia, and the mechanisms involved in the two series are discussed. These results emphasize the interest of the use of drugs interfering with DNA synthesis, in the field of teratology and in the experimental study of regressive evolution.