P₂, P₁, and P₀ myelin protein expression in developing rat sixth nerve: A quantitative immunocytochemical study

Abstract

Myelination and the expression of myelin proteins P2, P1, and P0 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 P0 glycoprotein and the basic proteins P1 and P2. 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-P0 immunoreactivity was found on sheaths with two and more compact lamellae; neither P1 nor P2 immunoreactivity was observed. On day 2, myelin sheaths with five and eight lamellae were stained respectively by anti-P1 and anti-P2. On day 3 the percentages of myelin sheaths stained were substantially higher: P0 95%, P1 78%, P2 15%. By day 4, anti-P0 and anti-P1 immunoreactivity was present in 95% of myelin sheaths; 35% were stained by anti-P2. For P2, staining intensity and percentage of myelin sheaths stained continued to increase and by day 20, 85% were anti-P2-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-P2. We conclude that the density and distribution of immunoreactivities of P0, P1, and P2 reflect their relative concentrations during myelin sheath development and growth. We attribute lack of detectable anti-P2 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 P2 basic protein.

Expression of myelin protein gene transcripts by schwann cells of regenerating nerve

“…This would correspond to the region in which we detected initial upregulation of mRNAs and suggests that transcription and translation o f myelin protein genes are closely re-lated during regeneration, as in normal development (Trapp et a]., 1987). During development, immunostainable Po is detectable before basic proteins (Hahn et al, 1987), although the convcrsc has been reported in regeneration using radiolabelled precursors with electrophoresis (Politis el al., 1982). Our results suggest that the timing of mRNAs for both Po and MBP are closely related, although the magnitudc of MBP upregulation, relative to the normal nerve, is much greater in segments undergoing myelination.…”

“…The localisation of mRNAs for Po, MBP, and MAG have been fully described prcviously (Trapp et al, 1987;Webster et al: 1987;. : 1989).…”

A role of peripheral myelin protein 2 in lipid homeostasis of myelinating schwann cells

“…By performing immunostaining on cross sections of sciatic nerves, we revealed a gradual expression of Pmp2, with a higher expression in myelin sheaths associated with large axons when compared with myelin sheaths associated with smaller axons. Only very few of the smallest myelin sheaths were not stained by Pmp2, which may be a consequence of a limitation of the labeling method, as suggested earlier (Hahn et al, 1987). However the level of expression of Pmp2 seems to be strictly regulated since the amount of expression can vary substantially in adjacent Schwann cells along the same axon.…”

Distribution of Myelin Basic Protein and P2 mRNAs in Rabbit Spinal Cord Oligodendrocytes

“…P2 mRNA has also been detected in rabbit spinal cord by Narayanan et al (1988). Recent evidence from studies on the rat sixth cranial nerve have provided evidence that, at least in this nerve, Pz is present in all the myelin sheaths in spite of previous views that P2 was absent from small myelinated fibers (Hahn et al, 1987). P2 and the MBPs are present on the cytoplasmic faces of compact myelin (Omlin et al, 1982;Trapp et al, 1984).…”