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P 2 , P 1 , and P 0 myelin protein expression in developing rat sixth nerve: A quantitative immunocytochemical study
Author(s) -
Hahn A. F.,
Whitaker J. N.,
Kachar B.,
deF. Webster H.
Publication year - 1987
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902600404
Subject(s) - myelin , axon , biology , staining , myelin sheath , anatomy , myelin basic protein , densitometry , antiserum , vibratome , immunocytochemistry , pathology , central nervous system , endocrinology , antibody , medicine , immunology , genetics
Myelination and the expression of myelin proteins P 2 , P 1 , and P 0 were studied quantitatively in the rat sixth cranial nerve during development. The postnatal development and growth of all myelin sheaths in this nerve have been studied morphometrically in a companion paper. Epon‐embedded blocks with closely matched topography in the transverse plane were selected from rats perfused at ages 1–4, 8, 15, and 20 days. From each block, serial semithin sections were cut, etched, and immunostained according to the peroxidase‐antiperoxidase method with well‐characterized polyclonal antisera that reacted specifically with P 0 glycoprotein and the basic proteins P 1 and P 2 . The immunoreactivities of individual myelin sheaths were measured by densitometry. Numbers of compact myelin lamellae, myelin spiral lengths, and axon diameters were determined on electronmicrographs of adjacent thin sections. At birth anti‐ P 0 immunoreactivity was found on sheaths with two and more compact lamellae; neither P 1 nor P 2 immunoreactivity was observed. On day 2, myelin sheaths with five and eight lamellae were stained respectively by anti‐ P 1 and anti‐ P 2 . On day 3 the percentages of myelin sheaths stained were substantially higher: P 0 95%, P 1 78%, P 2 15%. By day 4, anti‐ P 0 and anti‐ P 1 immunoreactivity was present in 95% of myelin sheaths; 35% were stained by anti‐ P 2 . For P 2 , staining intensity and percentage of myelin sheaths stained continued to increase and by day 20, 85% were anti‐ P 2 ‐positive. The density of immunoreactivity was not uniform in all myelin sheaths. At young ages staining varied with all three proteins. The variability decreased as myelin sheaths thickened; it persisted longest for anti‐ P 2 . We conclude that the density and distribution of immunoreactivities of P 0 , P 1 , and P 2 reflect their relative concentrations during myelin sheath development and growth. We attribute lack of detectable anti‐ P 2 immunoreactivity in some small sheaths at 20 days to their early stage of myelination and also to limitations of the method. We infer from our observations that all myelin‐forming Schwann cells express P 2 basic protein.