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S V Bryant

Publications and source records attributed to S V Bryant.

At least 55 records · Page 3Linked to original sources
PubMed1985

A quantitative analysis of regeneration from chimaeric limb stumps in the axolotl.

We have analysed the cellular contribution and cellular displacement which occur during regeneration from chimaeric (half triploid, half diploid) lower arms in the axolotl. In general both anterior and posterior halves contribute approximately 50% of the regenerated limb cells. Deviations from equal contribution were observed only when anterior tissue was grafted, suggesting that anterior tissue is more sensitive to grafting operations. Approximately 25% of all cells in the regenerated limb were found to be displaced to the opposite side of the limb. Cellular displacement was not random; 63% of all displaced cells were found in regions adjacent to the tissue of origin.

Ambystoma↗
PubMed1984

The distribution of marked dermal cells from small localized implants in limb regenerates.

Numerous experiments have demonstrated that skin has a profound influence on the pattern of limb regeneration in urodeles. In this investigation, the fate during regeneration of marked cells derived from narrow strips of skin inserted into different positions around the limb circumference has been followed. Skin strips were taken from triploid axolotls and transplanted into diploid sibling animals. The distribution of trinucleolate cells was determined at the site of amputation and in the regenerated limb. The results indicate that at the time of amputation marked cells appear to be localized to the graft, whereas in the regenerated marked cells may be found at all proximal-distal levels and at any position around the circumference of the limb. These results are discussed in terms of a possible mechanism for distal outgrowth.

Ambystoma↗
PubMed1984

Cellular contribution to supernumerary limbs in the axolotl, Ambystoma mexicanum.

Using the triploid cell marker, the cellular contribution from graft and stump to the supernumerary limbs which result from controlateral grafts of limb buds and regeneration blastemas in the axolotl has been analyzed. Grafts were made so as to appose anterior and posterior limb positions. Overall, the contribution from graft and stump tissue was found to be approximately equal although the position of the boundary between the two was variable from limb to limb. This result is consistent with models which suggest that intercalary regeneration is the driving force for patterning of the vertebrate limb. In addition, the pattern of cellular contribution to supernumerary limbs was consistently found to be asymmetrical in the dorsal-ventral axis. Hence, posterior limb tissue predominantly contributed cells to the posterior and dorsal part of the supernumerary limb whereas anterior limb tissue predominantly contributed cells to the anterior and ventral part of the supernumerary limb. The reason for this asymmetrical pattern remains unknown, but we suggest that it might result from a directional bias in intercalary regeneration, similar to that observed during intercalation in the proximal-distal axis of the urodele limb. Using the triploid cell marker in conjunction with a black/white pigmentation marker, the relationship between the cellular contribution boundary and the pigmentation boundary in supernumerary limbs has also been analyzed. It has been found that the positions of the two boundaries do not coincide, a result which suggests that the eventual location of pigment cells is not a good indicator of the location of nonpigment cells derived from graft and stump.

Aging↗
PubMed1984

Cellular contribution to supernumerary limbs resulting from the interaction between developing and regenerating tissues in the axolotl.

The relationship between limb development and limb regeneration is considered with regard to the mechanisms by which pattern is established during limb outgrowth. In a previous paper (Muneoka, K. and Bryant, S. V. 1982 Nature (London) 298, 369-371) the interaction between cells from the developing limb bud and the regenerating limb blastema was found to result in the production of organized supernumerary limb structures. In this paper the relative cellular contribution from developing and regenerating cells to supernumerary limbs resulting from contralateral grafts between limb buds and blastemas has been analyzed using the triploid cell marker in the axolotl. Results show that there is substantial participation from both developing and regenerating limb cells to all supernumerary limbs analyzed. These data lend further support to the hypothesis that developing and regenerating limbs utilize the same patterning mechanisms during limb outgrowth. This conclusion is discussed in terms of patterning models for developing and regenerating limbs and it is proposed that the rules of the polar coordinate model can best explain the behavior of cells during limb development as well as limb regeneration.

Ambystoma↗
PubMed1984

Improved techniques for use of the triploid cell marker in the axolotl, Ambystoma mexicanum.

Techniques for using the triploid cell marker for studying cell lineage during the development and regeneration of the axolotl limb are described. Triploid animals possess cells with three nucleoli while diploid animals possess cells with two nucleoli. We have developed a technique for isolating the limb dermis as a sheet of cells for whole-mount analysis of cellular ploidy. Whole-mount tissue preparations as well as paraffin-embedded sectioned tissues were stained specifically for nucleoli with bismuth. Cell counts from a number of triploid and diploid dermal preparations show that (1) diploid dermal cells never possess three nucleoli, (2) the frequency of trinucleolate cells in whole-mount triploid dermal preparations is not 100% but varies between animals from 30 to 76%, (3) within a single triploid animal, the frequency of trinucleolate cells in different dermal preparations is constant. These data establish the usefulness of this technique and emphasize the need for appropriate control cell counts when using the triploid cell marker in the axolotl.

Ambystoma↗
PubMed1982

Pattern regulation between hind- and forelimbs after blastema exchanges and skin grafts in Notophthalmus viridescens.

Experiments were performed to ascertain whether cells from the forelimb and the hindlimb of newts share a common pattern-regulating mechanism during regeneration. In one series of experiments early digit hindlimb and forelimb blastemas were exchanged either ipsilaterally or contralaterally. In a second experimental series, a strip of forelimb skin was added to a slit in a homologous site on the hindlimb or in a site 180 degrees removed from the position of origin, and vice versa (hindlimb skin into forelimb). After contralateral blastema exchanges, supernumerary limbs developed in addition to the limb of graft origin, whereas after ipsilateral exchanges, a single limb of graft origin regenerated. Limbs in which skin grafts were inserted into homologous sites developed normal regenerates of the host type, while in contrast, limbs with supernumerary digits regenerated from limbs which had received skin grafts in positions 180 degrees opposite to the homologous position. The results of both experiments were dependent on the positional disparity between the graft and host tissues, and they suggest that the forelimb and hindlimb do indeed utilize a common mechanism for pattern regulation.

Amputation, Surgical↗
PubMed1982

Evidence that patterning mechanisms in developing and regenerating limbs are the same.

Some amphibians have the ability to form new limbs throughout their lives. The essential similarity between limb regeneration and the original development of the limb is that both involve the elaboration of new patterns of structures. While some investigators believe that the two developing systems use similar mechanisms to generate the limb pattern, others have stressed the basic differences in developing the regenerating limbs, and have concluded that different mechanisms exist. Both developing and regenerating urodele limbs can be caused to form supernumerary parts following tissue misalignment so that cells from normally disparate positions within the limb circumference confront each other (developing limbs; regenerating limbs, see ref. 11 for review). If similar mechanisms are operating, the developing limb should respond to grafts of regenerating limb tissue, and vice versa, by forming supernumerary outgrowths. If different mechanisms are operating, either the grafts should fail or the response should be disorganized. Our results with the axolotl Ambystoma mexicanum suggest that the patterning mechanisms are the same.

Ambystoma↗
PubMed1981

Studies of digit regeneration and their implications for theories of development and evolution of vertebrate limbs.

Simple amputation of various combinations of hindlimb digits of Notophthalmus viridescens resulted in a variety of abnormal regenerates. The abnormalities included the formation of adventitious digits and branched digits, fusion between digits, and increases and decreases in the normal number of phalanges. The type of abnormality was correlated with the proximal-distal level of amputation and with the identity of the digits removed. These results are discussed in the context of a model for normal digit formation. An important feature of this model is that the normal regeneration of separate digits is dependent upon precise and orderly interactions between different parts of the limb circumference. In the experiments we report, the disruption of these orderly interactions leads to a variety of abnormalities. In addition, the model for digit formation presented here is discussed in light of its implications for evolutionary trends in the tetrapod limb.

Amputation, Surgical↗
PubMed1979

Interactions between irradiated and unirradiated tissues during supernumerary limb formation in the newt.

The interactions between irradiated and unirradiated blastemas and stumps in the newt forelimb were studied. Irradiated right blastemas at the stage of early digits were grafted to unirradiated left stumps and unirradiated left blastemas were grafted to irradiated right stumps. Grafts were oriented with their anterior-posterior axes opposed to that of the stumps. Supernumerary limbs ranging in completeness from one to four digits were found to arise predominantly on the anterior or posterior sides of the host limb. The graft developed well when the blastema was unirradiated and had reversed handedness with respect to the stump. Irradiated grafts developed poorly. On occasions, limbs with two supernumerary structures were found. The results are discussed in terms of the origin of the cells which comprise the supernumerary limbs and their bearing on a recently presented model concerned with pattern specification and regulation in epimorphic fields.

Animals↗
PubMed1978

Regenerative ability of double-half and half upper arms in the newt, Notophthalmus viridescens.

The upper arms of adult newts (Notophthalmus viridescens) were surgically manipulated to create double-half dorsal, double-half ventral, double-half anterior, and double-half posterior upper arms, and longitudinal half-dorsal, half-ventral, half-anterior, and half-posterior upper arms. Amputation through the double-half upper arms usually failed to elicit normal distal regeneration, despite the fact that an apparently normal regeneration blastema was initially formed. Instead, regeneration in these cases was limited to the formation of a variable number of small cartilage elements. On the basis of these results it is concluded that a complete limb circumference is required for distal transformation in newts, in addition to the well-established requirements for a wound epidermis, adequate innervation and dedifferentiation leading to blastema formation. A model for the sequential generation of new parts of the limb pattern during distal transformation from a complete circumference is presented. This model can also account for the occurrence of normal early stages of regeneration in double-half upper arms. Half upper arms which were amputated immediately were shown to develop single, complete regenerates. If amputation of half upper arms was delayed three or more weeks to permit complete wound healing, a supernumerary limb from the lateral wound surface sometimes developed in addition to a complete, single limb from the distal amputation surface.

Amputation, Surgical↗
PubMed1976

Pattern regulation in epimorphic fields.

We have described a formal model for pattern regulation in epimorphic fields in which positional information is specified in terms of polar coordinates in two dimensions. We propose that cells within epimorphic fields behave according to two simple rules, the shortest intercalation rule and the complete circle rule, for both of which there is direct experimental evidence. It is possible to understand a large number of different behaviors of epimorphic fields as a straight-forward consequence of these two rules, and the model therefore provides a context in which to view many of the results of experimental embryology. Although we have confined our discussion to cockroach legs, the imaginal disks of Drosophila, and regenerating and developing amphibian limbs, the fact that the model can explain regulative behavior in such evolutionarily diverse animals suggests that it may have general applicability to epimorphic fields. The predictions which the model makes should make it possible to assess its applicability to other developing systems, and to investigate the cellular mechanisms involved.

Amphibians↗