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Biomedical subjects

M Maden

Publications and source records attributed to M Maden.

At least 91 records · Page 5Linked to original sources
PubMed1986

Retinoic acid-binding protein in the chick limb bud: identification at developmental stages and binding affinities of various retinoids.

The application of retinoic acid (RA) to the developing chick limb bud causes 6-digit double posterior limbs to form instead of the normal 3-digit limb. As an attempt to begin a molecular analysis of this phenomenon we have identified and characterized a soluble cytoplasmic receptor for RA, namely cytoplasmic retinoic acid-binding protein (CRABP), from the cells of the chick limb bud. It is present from stages 20-35 at similar levels and has an apparent Kd of 140-280 nM. In competition experiments with other retinoids Ro 13-7410 was found to be the most effective at competing for sites on CRABP followed by all-trans-RA, 13-cis-RA, Ro 10-1670 and retinal. Retinol, retinyl palmitate, retinyl acetate, etretinate and arotinoid showed low or no affinity for CRABP. Specificity for binding was thus demonstrated since analogues with an acid end group competed effectively, the aldehyde competed less effectively and the ester or alcohol groups did not compete. At the concentration of RA that needs to be administered to cause duplications in the pattern of the limb bud, we estimate that 4% of the CRABP present in the limb bud has RA bound. The similarities between steroid receptors in the mediation of steroid hormone action and CRABP in the mediation of RA action is discussed. In this regard we note that while there are 10(4) steroid receptors per cell in other cell types we estimate that there are about 10(5) RA receptors per cell in the chick limb bud.

Animals↗
PubMed1986

Comparison of the effects of vitamin A on limb development and regeneration in the axolotl, Ambystoma mexicanum.

The objective of this investigation was to compare the effect of vitamin A on limb development and limb regeneration in the same animal, at the same time, thus eliminating the possibility that species differences or different rates of uptake between animals would influence the results. Axolotl larvae had both right limbs amputated and then were treated with retinol palmitate by immersion at 60 or 300 mg l-1 for 4 or 10 days. Intact left developing limbs at the cone, two-digit, or four-digit stages responded to the treatment by deletion of skeletal elements producing hypomorphic limbs. Severity of the deletions was correlated with higher dose, longer times, and earlier stages of limb development. In contralateral right regenerating limbs, the effect of the same treatment was to cause various degrees of proximodistal duplication as well as occasional hypomorphic regenerates. Thus, there is a marked difference in response to vitamin A between developing and regenerating limbs. The implications of this observation are discussed especially with respect to the underlying morphogenetic mechanisms.

Ambystoma mexicanum↗
PubMed1986

Comparison of the effects of vitamin A on limb development and regeneration in Xenopus laevis tadpoles.

The purpose of these experiments was to compare the effects of vitamin A on developing and regenerating limbs in Xenopus laevis tadpoles. Each tadpole had one hindlimb amputated to induce regeneration while the contralateral developing limb was left intact. Tadpoles at stages 50 through 54 were treated by immersion in retinol palmitate at doses ranging from 0.3 to 75 i.u. ml-1, for periods ranging from 1 to 14 days. Developing limbs usually became hypomorphic as a result of the treatment, with results varying with stage and treatment from slight phalange derangements to total disruption of pattern, or complete inhibition of limb development. Regenerating limbs gave a variety of responses including hypomorphic regeneration, proximodistal or anteroposterior duplication of skeletal elements, or complete suppression of regeneration. The response to retinol palmitate of developing limbs was clearly different from regenerating limbs. Hypotheses which might explain the results were discussed and a hypothesis which proposed a dual action of vitamin A affecting both the cell cycle and the mechanism of pattern regulation was proposed.

Animals↗
PubMed1986

The effects of local application of retinoic acid on limb development and regeneration in tadpoles of Xenopus laevis.

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 right hindlimb 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.

Animals↗
PubMed1985

Motorneuron pools innervating muscles in vitamin A-induced proximal-distal duplicate limbs in the axolotl.

Serially duplicated limbs containing two sets of proximal muscles were created in axolotls by vitamin A treatment. The innervation of three replicated proximal muscles was studied by using retrograde transport of horseradish peroxidase. These were the forelimb muscles biceps (seven cases) and anconeus (five cases) and the hindlimb muscle puboischiotibialis (five cases). In two cases (both of anconeus) innervation was from a correct motorneuron pool. In the other 15 cases the innervation was from an incorrect, distal limb muscle, motorneuron pool. These results are interpreted as evidence against long range signals between nerve and muscle controlling specific nerve regeneration. However, the data are compatible with models of axonal guidance that use local pathway cues.

Ambystoma↗
PubMed1985

Retinoids and the control of pattern in regenerating limbs.

It has recently been discovered that, as well as having effects on cell division and differentiation, retinoids induce dramatic changes in the development of pattern in limbs. Local application of retinoic acid to the anterior side of chick limb buds causes anteroposterior mirror-imaging such that the limb has six digits instead of three. In Rana limb buds retinoids induce changes in both the anteroposterior and proximodistal axes. In regenerating axolotl limbs their effect is primarily on the proximodistal axis. These proximodistal effects result in the regeneration of a complete limb from distal amputation levels. Concentration effects, time effects and the relative efficacy of various retinoids have been established. Cellular changes observed include a stimulation of epidermal mucopolysaccharide production, inhibition of cell division, induction of cartilage matrix breakdown and a stimulation of fibronectin production by mesodermal cells. The relevance of each of these changes to pattern effects has been determined. Initial experiments on the cellular location of radiolabelled retinoic acid are described. It thus seems that retinoids can change the determination of developing cells, and once we know the molecular basis of retinoid action then we should also know how developing cells become specified to form particular cell types.

Ambystoma↗
PubMed1984

The cellular contributions of blastema and stump to 180 degrees supernumerary limbs in the axolotl.

By inverting triploid blastemas onto diploid stumps (and vice versa) the cellular contributions to supernumerary limbs so generated have been assessed. The four classes of 180 degrees supernumerary limbs each had a different mixture of stump and blastemal cells. The mesoderm of normal supernumeraries was composed entirely or almost entirely of stump cells and were always of stump handedness. The mesoderm of symmetrical supernumeraries was of variable composition, it could be mostly stump, mostly blastema or half and half. In part normal/part symmetrical supernumeraries the normal part was usually of stump origin and the aberrant symmetrical part of blastemal origin. In part normal/part inverted supernumeraries the normal part came from the stump and the inverted part from the inverted blastema. The handedness of each part of these supernumeraries corresponded with its cellular origin. The epidermis of the supernumeraries was not of the same relative composition as the mesoderm, it tended to have a larger stump component. The black/white marker was also used and this too tended not to conform to the mesodermal contribution patterns. These results are discussed in terms of rules for generating supernumeraries and it is concluded that with the exception of symmetrical supernumeraries the cellular contributions of stump and blastema determine their structure.

Ambystoma↗
PubMed1983

The effect of vitamin A on limb regeneration in Rana temporaria.

Previous experiments in which vitamin A has been administered to developing or regenerating limbs have shown that different limb axes are affected. In regenerating axolotl limbs, serial reduplications in the proximodistal axis are produced. In the developing chick limb bud, mirror-imaged reduplications in the anteroposterior axis are produced. Results reported here on Rana temporaria limb buds reveal that vitamin A causes both effects to occur. That is, limbs are both serially reduplicated in the proximodistal axis and mirror imaged in the anteroposterior axis. Time and concentration effects are explored and the significance of these results for our current understanding of axial organisation in limbs is discussed.

Animals↗
PubMed1983

A test of the predictions of the boundary model regarding supernumerary limb structure.

The model proposed in the preceding paper (Meinhardt, 1983) makes specific predictions about the handedness of supernumerary limbs generated after 180 degrees rotation of blastemas. These predictions are tested here by re-examining, in detail, the structure of 100 of these supernumeraries. Of the four predictions, only one was found not to hold. The other three are remarkably precise in their predictions and fit perfectly with the data. A possible reason for the failure of this one prediction is suggested.

Ambystoma↗
PubMed1983

The effect of vitamin A on the regenerating axolotl limb.

These experiments describe further investigations into the effects of vitamin A on regenerating limbs. The effects of different retinoids, the time of administration, concentration of vitamin A and histological, autoradiographic and histochemical studies are reported. The most obvious result of vitamin A treatment is to cause proximal elements to regenerate from distal amputation levels, that is to cause serial reduplication of pattern in the proximodistal axis. Retinoic acid was the most potent of the analogues tested and longer times of administration or higher concentrations cause a greater amount of serial reduplication. Various tissue changes have been found which include the inhibition of cell division, loss of cartilage metachromasia, changes in the mucous-secreting properties of the epidermis and an increased packing in the blastemal cells. The significance of these cellular effects in relation to the pattern-formation changes is discussed.

Ambystoma mexicanum↗
PubMed1982

Axial organization of the regenerating limb: asymmetrical behaviour following skin transplantation.

An extensive series of skin grafting operations has been performed to investigate axial organization in the regenerating axolotl limb. Semicircular cuffs of skin from either anterior, posterior, dorsal or ventral surfaces were exchanged between right and left limbs thereby creating limbs with double anterior, double posterior, double dorsal or double ventral skin, all with normal internal tissues. Both fore and hindlimbs were used at both upper and lower limb levels. Following amputation through the grafted region the resulting regenerates were analysed both by whole-mount cartilage staining to observe the pattern of digits and by serial sectioning to observe the pattern of muscles. There were clear asymmetries in ability to produce duplications - posterior to anterior grafts resulted in a consistently high frequency of digital duplications, whereas anterior to posterior grafts produced very few. Similarly, dorsal to ventral grafts resulted in a good frequency of muscle duplications, whereas ventral to dorsal grafts did not. Such asymmetrical behavior is not predicted by most models involving local cell:cell interactions and the significance of the results for theories of pattern formation is discussed.

Ambystoma mexicanum↗
PubMed1981

Experiments on Anuran limb buds and their significance for principles of vertebrate limb development.

A standard set of six experiments performed on the limb buds of two species of Anurans - Rana temporaria and Xenopus laevis - are described. The experiments are limb-bud amputation, distal to proximal shifts, proximal to distal shifts, inversion of the dorsoventral axis inversion of the anteroposterior axis and inversion of both axes. The results are compared to those previously reported for Urodeles and chicks to determine whether any principles of vertebrate limb development can be formulated. It appears that the proximodistal axis becomes increasingly mosaic from the Urodeles through Anurans to chicks. In the transverse axes however, there is much more uniformity of behaviour in the production of supernumerary limbs. The relation between the type of limb development (regulative or mosaic) and the subsequent regenerative powers of the adult limb is discussed.

Amputation, Surgical↗