Increased slow transport in axons of regenerating newt limbs after a nerve conditioning lesion.
We have previously shown that a nerve conditioning lesion (CL) made 2 weeks prior to amputation results in an earlier onset of limb regeneration in newts. Studies in fish and mammals demonstrate that when a CL precedes a nerve testing lesion, slow component b (SCb) of axonal transport is increased compared to axons that had not received a CL. We wanted to know whether the earlier initiation of limb regeneration after a CL was associated with an increase in SCb transport. The transport of [35S]methionine labeled SCb proteins was measured by using SDS-PAGE, fluorography, and scintillation counting. The rate of transport and quantity of SCb proteins was determined at 7, 14, 21, and 28 days after injection of [35S]methionine into the motor columns of normal; single lesioned (i.e., transection axotomy, amputation axotomy, or sham CL followed by amputation); and double-lesioned limb axons (i.e., nerve transection CL followed 2 weeks later by amputation axotomy). The rate of SCb transport in axons of unamputated newt limbs was 0.19 mm/day. There was an increase in the amount of labeled SCb proteins transported in axons regenerating as the result of a single lesion but no acceleration in the rate of SCb transport, which was 0.21 mm/day in axons that received a sham CL followed by limb amputation. The rate of SCb transport doubled (0.40 mm/day) and the amount of labeled SCb proteins being transported was increased when amputation was preceded by a CL. This study demonstrates that the earlier onset of limb regrowth, seen when amputation follows a CL, is associated with an increased transport of SCb proteins. This suggests that limb regeneration is, in part, regulated by axonal regrowth. We propose that the blastema requires a minimum quantity of innervation before progressing to the next stage of limb regeneration, and that the transport of SCb proteins determines when that quantity will be available.
Maier
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CE
Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, Ohio.
McQuarrie
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D000199:Actins / Q000493:pharmacokinetics; D000818:Animals; D001369:Axons / Q000502:physiology*; D002147:Calmodulin / Q000493:pharmacokinetics; D002352:Carrier Proteins / Q000493:pharmacokinetics; D004591:Electrophoresis, Polyacrylamide Gel; D005121:Extremities / Q000502:physiology*; D008840:Microfilament Proteins / Q000493:pharmacokinetics; D008869:Microtubule-Associated Proteins / Q000493:pharmacokinetics; D012038:Regeneration; D012455:Salamandridae; D014404:Tubulin / Q000493:pharmacokinetics; D013049:Spectrin
D000199:Actins; D002147:Calmodulin; D002352:Carrier Proteins; D008840:Microfilament Proteins; D008869:Microtubule-Associated Proteins; D014404:Tubulin; D013049:Spectrin