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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Developmental Dynamics 198 (1993), S. 77-85 
    ISSN: 1058-8388
    Keywords: Limb regeneration ; Retinoic acid ; Positional identity ; Pattern formation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Previous studies have shown that in axolotls (Ambystoma mexicanum), retinoic acid (RA) treatment evokes pattern completion in limb regenrates derived from anterior and dorsal half zeugopodia (lower arms and legs), but causes regenerative failure in posterior and ventral half zeugopodia. Pattern completion in anterior and dorsal half limbs may be explained by postulating that intercalary regeneration occurs in the anteroposterior (AP) and dorsoventral (DV) axes between blastema cells that are posteriorized (anterior half limb) or ventralized (dorsal half limb) by RA, and circumferential anterodorsal cells that remain unaffected by RA and thus maintain their original positional indentities. The contrasting regenerative failure of RA-treated posterior and ventral half zeugopodia may likewise be explained by postulating that all the blastema cells in the posterior half are posteriorized, and all the cells in the ventral half are ventralized by RA, thus eliminating differentials in transverse positional identity essential for blastema formation and outgrowth. To test these postulates we grafted blastemas derived from limbs halved in the AP and DV axes of control and RA-treated animals to untreated whole limb stumps and analyzed the patterns of supernumerary (SN) regeneration. The site or location of SN formation will demonstrate (1) whether RA has posteriorized and ventralized the positional identity of the blastema cells and (2) if blastema cells in the periphery of the anterodorsal quadrant of the limb are resistant to these RA-induced changes in positional identity. Our results are consistent with a model in which RA posteriorizes positional identity in both halves of the anteroposterior axis and ventralizes it in both halves of the dorsoventral axis, while circumferential anterodorsal cells maintain their original positional identities. In addition, this model can explain why systemically administered RA in urodeles does not induce transverse axial duplications in zeugopodial regenerates of whole limbs, like it does in regenerating anuran and developing chick limb buds. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0002-9106
    Keywords: Regeneration ; Retinoic Acid ; Dose-Dependency ; AP axis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Retinoic acid (RA) induces pattern duplication in the proximodistal (PD) axis of axolotl limb regenerates. The effect is dose-dependent, with the maximum extent of duplication being evoked at a dose of 150 μ RA/g body weight, The same dose of RA induces maximum pattern completion in the anteroposterior (AP) axis of regenerating anterior half or double anterior half limbs. RA inhibits the regeneration of posterior half or double posterior half limbs (Kim, W.S., and Stocum, D.L. [1986] Dev Biol 114:170-179). The effects of lower doses of RA on the AP axis of limb regenerates have not been tested and thus it is not known whether the effects of RA on positional identity in this axis are dose-dependent or are all-or-none. To answer this question, we examined the effects of a range of doses of RA on AP positional identity in regenerating double anterior and double posterior axolotl forelimbs and hindlimbs constructed by exchanging the anterior and posterior halves of right and left zeugopodia as either autografts or homografts. Ten days after the exchange, the double half zeugopodia were amputated through their distal ends. At 4 days postamputation, the animals were injected intraperitoneally with 20, 50, 75, or 100 μg RA/g body weight and the constructs allowed to regenerate for at least 6 weeks. Control double anterior forelimbs and hindlimbs formed symmetrical regenerates with an average of two and 1.8 anterior digits, respectively. RA treatment induced the blastema of double anterior zeugopodia to regenerate missing posterior structures in mirror-image patterns and to duplicate zeugopodial and stylopodial elements in the PD axis. The extent of posterior regeneration and PD duplication was proportional to dose. Control double posterior forelimbs and hindlimbs produced symmetrical regenerates with an average of 2.4 and 3.3 posterior digits, respectively. Regeneration was inhibited at 100% frequency at doses above 50 μg of RA, but regeneration took place with increasing frequency at the 50 and 20 μg doses. We conclude from these data that RA posteriorizes AP positional identity in a dose-dependent way, analogous to the dose-dependent proximalization of positional identity reported previously for the PD axis. © 1992 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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