Expression of a developmentally regulated, phosphorylated isoform of microtubule-associated protein 1B in regenerating axons of the sciatic nerve.
Monoclonal antibodies SMI-31 and 150 recognize phosphorylation epitopes on microtubule-associated protein 1B that have been shown to be developmentally down-regulated in the nervous system. We have used these antibodies to establish changes in the pattern of expression of their epitopes on microtubule-associated protein 1B in regenerating axons of the sciatic nerves in the adult mouse and rat. Immunohistochemical studies showed that, in the sciatic nerve, regenerating axons in both adult mice and rats were labelled with monoclonal antibody 150 in a proximodistal gradient which was highest at the growth cone. This is the first report of expression of a developmentally regulated, phosphorylated isoform of microtubule-associated protein 1B in regenerating axons. Immunoblotting showed that the expression of the isoform recognized by monoclonal antibody 150 is present in normal adult mouse sciatic nerve and in regenerating axons following crush or cut lesions, but was not detectable in the normal or regenerating adult rat peripheral nervous system. Regenerating axons were also labelled by monoclonal antibody SMI-31, but the labelling, unlike antibody 150 labelling, was uniform along the entire length of the axon and immunoblotting showed that it was due to recognition of neurofilament protein. We conclude that the phosphorylated isoforms of microtubule-associated protein 1B recognized by monoclonal antibody 150 that are developmentally down-regulated in the adult rat central and peripheral nervous systems and adult mouse cerebellum are maintained in the normal peripheral nervous system of the adult mouse. When peripheral axons regenerate in the adult mouse, the regenerating axons also contain these isoforms. Adult rat regenerating axons are stained by antibody 150 only in tissue sections, not in immunoblots. The maintenance of immature isoforms of microtubule-associated protein 1B in mouse peripheral axons may relate to a continual capacity for growth and remodelling. The immunohistochemical localization of the antibody 150 epitope in growth cone-like structures and sprouts in injured nerves shows that phosphorylation of microtubule-associated protein 1B is likely to be an integral part of the regenerative response. These results also show that the phosphorylation epitopes on microtubule-associated protein 1B recognized by monoclonal antibodies 150 and SMI-31 are different and that only expression of the former correlates with axonal regeneration.
Bush
M S
MS
Developmental Biology Research Centre, Randall Institute, King's College London, U.K.
Tonge
D A
DA
Woolf
C
C
Gordon-Weeks
P R
PR
D000818:Animals; D000911:Antibodies, Monoclonal; D001369:Axons / Q000502:physiology* / Q000648:ultrastructure; D002531:Cerebellum / Q000378:metabolism / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D007124:Immunoenzyme Techniques; D007150:Immunohistochemistry; D051379:Mice; D008815:Mice, Inbred Strains; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis*; D009416:Nerve Regeneration; D010766:Phosphorylation; D051381:Rats; D012584:Sciatic Nerve / Q000166:cytology / Q000502:physiology*; D013116:Spinal Cord / Q000378:metabolism / Q000502:physiology*
D000911:Antibodies, Monoclonal; D008869:Microtubule-Associated Proteins; C085284:microtubule-associated protein 1B