Isolation and Characterization of the Myelin‐Like Membranes Ensheathing Giant Axons in the Earthworm Nerve Cord<sup>a</sup>

Roots, Betty I.; Cardone, Beatrice; Pereyra, Pedro M.

doi:10.1111/j.1749-6632.1991.tb15660.x

Cited by 9 publications

(8 citation statements)

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“…Another interesting observation is that looking at the evolutionary trees from crustacean, annelid and craniate, it is clear that as proposed by B. Roots, the synthesis by glial cells of these multilamellar sheath of membrane has occurred separately and at least on three different occasion (Roots et al, 1991). This would have happen in canaloid copepod for the crustaceans, and earthworm for annelid.…”

Section: In Vertebrate Myelin Was Acquired By Placodermsmentioning

confidence: 92%

The acquisition of myelin: An evolutionary perspective

Zalc

2016

Brain Research

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It has been postulated that the emergence of vertebrates was made possible by the acquisition of neural crest cells, which then led to the development of evolutionarily advantageous complex head structures (Gans and Northcutt, 1983). In this regard the contribution of one important neural crest derivative-the peripheral myelin sheath-to the success of the vertebrates has to be pointed out. Without this structure, the vertebrates, as we know them, simply could not exist. After briefly reviewing the major functions of the myelin sheath we will ask and provide tentative answers to the following three questions: when during evolution has myelin first appeared? Where has myelin initially appeared: in the CNS or in the PNS? Was it necessary to acquire a new cell type to form a myelin sheath? Careful examination of fossils lead us to conclude that myelin was acquired 425 MY ago by placoderms, the earliest hinge-jaw fishes. I argue that the acquisition of myelin during evolution has been a necessary prerequisite to permit gigantism of gnathostome species, including the sauropods. I propose that this acquisition occurred simultaneously in the PNS and CNS and that myelin forming cells are the descendants of ensheathing glia, already present in invertebrates, that have adapted their potential to synthesize large amount of membrane in response to axonal requirements. This article is part of a Special Issue entitled SI: Myelin Evolution.

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Section: In Vertebrate Myelin Was Acquired By Placodermsmentioning

confidence: 92%

The acquisition of myelin: An evolutionary perspective

Zalc

2016

Brain Research

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“…The protein composition of invertebrate myelin is obscure. Some components have been identified on electrophoresis which appear to be unrelated to any of the vertebrate proteins [39,54], but almost nothing is known of their function. This is clearly an area where further research would be beneficial; we can speculate that a better understanding of the genetics of invertebrate myelination might shed light on why molluscs and insects have not developed myelin.…”

Section: Molecular Evidencementioning

confidence: 99%

The Evolution of Myelin: Theories and Application to Human Disease

Knowles¹

2017

J Evol Med

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Myelin, once thought of as a simple insulating sheath, is now known to be a complex, dynamic structure. It has multiple functions in addition to increasing conduction velocity, including reducing the energetic cost of action potentials, saving space, and metabolic functions. Myelin is also notable for likely having arisen independently at least three times over the course of evolutionary history. This article reviews the available evidence about the evolution of myelin and proposes a hypothesis of how it arose in vertebrates. It then discusses the evolutionary trade-offs associated with myelination and suggests a possible animal model for further study of this phenomenon. Finally, it briefly covers the neural regulation of myelination before discussing possible roles of myelin in human social cognition and evolution, and the relevance of this to human disease.

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“…In contrast to the heavily myelinated axons produced by Schwann cells in the mammalian peripheral nervous system, invertebrate axons are surrounded by glia that either do not produce myelin, such as in C elegans [ 8 ] , crayfish [ 10 ], and leeches [ 11 ], or produce a thin layer of myelin, like earthworms [ 12 ]. This begs the question as to whether the presence of heavily myelinated axons could be one factor potentially inhibiting axon auto-fusion in mammals, as myelin is a known inhibitor of nerve regeneration [ 13 ].…”

Section: Introductionmentioning

confidence: 99%

Closing the Gap Between Mammalian and Invertebrate Peripheral Nerve Injury: Protocol for a Novel Nerve Repair

Vest¹,

Guida²,

Colombini³

et al. 2020

JMIR Res Protoc

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Background Outcomes after peripheral nerve injuries are poor despite current nerve repair techniques. Currently, there is no conclusive evidence that mammalian axons are capable of spontaneous fusion after transection. Notably, certain invertebrate species are able to auto-fuse after transection. Although mammalian axonal auto-fusion has not been observed experimentally, no mammalian study to date has demonstrated regenerating axolemmal membranes contacting intact distal segment axolemmal membranes to determine whether mammalian peripheral nerve axons have the intrinsic mechanisms necessary to auto-fuse after transection. Objective This study aims to assess fusion competence between regenerating axons and intact distal segment axons by enhancing axon regeneration, delaying Wallerian degeneration, limiting the immune response, and preventing myelin obstruction. Methods This study will use a rat sciatic nerve model to evaluate the effects of a novel peripheral nerve repair protocol on behavioral, electrophysiologic, and morphologic parameters. This protocol consists of a variety of preoperative, intraoperative, and postoperative interventions. Fusion will be assessed with electrophysiological conduction of action potentials across the repaired transection site. Axon-axon contact will be assessed with transmission electron microscopy. Behavioral recovery will be analyzed with the sciatic functional index. A total of 36 rats will be used for this study. The experimental group will use 24 rats and the negative control group will use 12 rats. For both the experimental and negative control groups, there will be both a behavior group and another group that will undergo electrophysiological and morphological analysis. The primary end point will be the presence or absence of action potentials across the lesion site. Secondary end points will include behavioral recovery with the sciatic functional index and morphological analysis of axon-axon contact between regenerating axons and intact distal segment axons. Results The author is in the process of grant funding and institutional review board approval as of March 2020. The final follow-up will be completed by December 2021. Conclusions In this study, the efficacy of the proposed novel peripheral nerve repair protocol will be evaluated using behavioral and electrophysiologic parameters. The author believes this study will provide information regarding whether spontaneous axon fusion is possible in mammals under the proper conditions. This information could potentially be translated to clinical trials if successful to improve outcomes after peripheral nerve injury. International Registered Report Identifier (IRRID) PRR1-10.2196/18706

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Isolation and Characterization of the Myelin‐Like Membranes Ensheathing Giant Axons in the Earthworm Nerve Cord^a

Cited by 9 publications

References 4 publications

The acquisition of myelin: An evolutionary perspective

The acquisition of myelin: An evolutionary perspective

The Evolution of Myelin: Theories and Application to Human Disease

Closing the Gap Between Mammalian and Invertebrate Peripheral Nerve Injury: Protocol for a Novel Nerve Repair

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Isolation and Characterization of the Myelin‐Like Membranes Ensheathing Giant Axons in the Earthworm Nerve Corda

Cited by 9 publications

References 4 publications

The acquisition of myelin: An evolutionary perspective

The acquisition of myelin: An evolutionary perspective

The Evolution of Myelin: Theories and Application to Human Disease

Closing the Gap Between Mammalian and Invertebrate Peripheral Nerve Injury: Protocol for a Novel Nerve Repair

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Isolation and Characterization of the Myelin‐Like Membranes Ensheathing Giant Axons in the Earthworm Nerve Cord^a