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The effects of local application of retinoic acid on limb development and regeneration in tadpoles of Xenopus laevis.
Scadding SR
,
Maden M
.
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Vitamin A can have different effects on developing and regenerating limbs depending on the mode of administration. Previous work has demonstrated the differential effect of retinol palmitate on limb development and regeneration in Xenopus laevis. The purpose of the present investigation was to determine the effects of vitamin A on limb development and regeneration in Xenopus when administered by a local implantation method. Xenopus tadpoles had both hindlimbs implanted with either a block of silastin carrying retinoic acid or an anion exchange resin bead carrying retinoic acid and then the righthindlimb was amputated and the effect of the retinoic acid on limb development and regeneration was studied. The results showed that in developing hindlimbs the effects of silastin implants carrying retinoic acid was to cause skeletal reductions or deletions similar to those induced by immersion of the tadpole in retinol palmitate. On the other hand, in regenerating hindlimbs, the silastin implants caused a range of skeletal reductions and deletions as well as occasional accessory structures but notably induced no proximodistal (PD) duplications, unlike the effect of immersion in retinol palmitate where PD duplications were a common response. Implantation of anion exchange resin beads carrying retinoic acid had no significant effect on either development or regeneration beyond stage 50, presumably because the dose of the retinoic acid was so low. Thus the results suggest that the mode of administration of vitamin A has a very significant influence on its effects. The significance of this observation for vitamin A experiments on limbs is discussed.
Fig. 1. (A) Lateral view of a lefthindlimb of a tadpole implanted with a control silastin block (arrowhead) at stage 52. Limb development was completely normal. The limb consisted of femur (Fe), fusing tibia (T) and fibula (F), tibiale (t) and fibulare ( / ) , five tarsals (ta) (of which only three are visible here), five metatarsals {mi), and 14 phalanges arranged on digits I through V in the formula 2-2-3-4-3. Digit V (V) is dorsal (on right in photomicrograph). x8. (B) Ventral view of the hindlimbs of a tadpole implanted with retinoic acid silastin blocks (arrowheads) at stage 52. In both the developing left (L) hindlimb and regenerating right (R) hindlimb, the femur and tibia-fibula were quite defective, and yet both feet were entirely normal. x8. (C) Ventral view of the hindlimbs of a tadpole implanted with retinoic acid silastin blocks at stage 52. The left (L) developing hindlimb lacked distalfemur, tibia-fibula, and proximal parts of tibiale and fibulare. Foot was moderately hypomorphic as well, with only three digits. The right (R) regenerating limb had a defective regenerate in which most of the leg was absent and yet the regenerated foot possessed 13 digits forming a ring as they emerge from an irregular set of tarsals. x8. (D) Lateral view of a lefthindlimb of a tadpole implanted with a retinoic acid silastin block at stage 53. The implant (arrowhead) came to lie in the region of the prospective fibula leading to the complete deletion of the element. The rest of the limb including the tibia (T) was apparently normal. Digit V (V) is dorsal. x9. (E) Lateral view of a regenerated righthindlimb of a tadpole implanted with a retinoic acid silastin block (arrowhead) at stage 54. The leg was quite defective with a shortened femur, and completely irregular tibia-fibula and tibiale-fibulare. The four-digithand was quite typical of regeneration subsequent to amputation at stage 54. Digit V (V) is dorsal. xl3. (F) Ventral view of the hindlimbs of a tadpole implanted with retinoic acid silastin blocks (arrowhead) at stage 52. In the developing left (L) hindlimb the femur, tibia-fibula, and tibiale-fibulare were largely fused into a continuous bent cartilage rod ending in a slightly hypomorphic four-digitfoot. The right (R) hindlimb regenerate was completely hypomorphic and ended in a single digit. x7. (G) Ventral view of the hindlimb of a tadpole implanted with retinoic acid silastin blocks at stage 53. The left (L) developing limb is greatly reduced with only two digits attached to the end of the femur. The right (R) regenerating limb has completely failed to regenerate. Only a V- shaped piece of cartilage is present beyond the femur and this probably represents a deformed stump tibia-fibula. xlO.
Fig. 2. Ventral view of the hindlimb region of a tadpole implanted with retinoic acid ion exchange beads at stage 50. The left developing hindlimb (L) is essentially normal as is the regenerated righthindlimb (R). The accessory limb (A) arises from an accessory pelvic girdle (g). In the accessory limb, the zeugopodium consists of three fused rods (tibia-fibula-tibia?) and the foot has seven somewhat irregular digits. x9.
