Immunocytochemical study of the appearance of P₂ in developing rat peripheral nerve: comparison with other myelin components

Summary

Using indirect immunofluorescence on both dissociated cell cultures and frozen sections from rat sciatic nerve, dorsal root ganglion and superior cervical ganglion, we have examined the development and distribution of the peripheral myelin protein P₂. It first appears in development in sciatic nerve and dorsal root ganglion on the first day after birth, at about the same time as P₀ and P₁. Like galactocerebroside, P₀ and P₁, P₂ disappears gradually from dissociated Schwann cells in culture. In adult sciatic nerve, and dorsal and ventral roots, it shows an uneven distribution and is absent from some myelinated axons. In electron micrographs the onset of myelination in the sciatic nerve occurs between the day of birth (day 0) and the first day after birth (day 1). Immunofluorescence studies on freshly dissociated cell suspensions, frozen sections and dissociated cell cultures at these early time points indicate that the myelin glycolipids galactocerebroside and sulphatide are present on the surface of many Schwann cells at least one day before myelination starts while the myelin proteins P₀, P₁ and P₂ are not detected until myelination begins. This suggests that the early appearance of galactocerebroside and sulphatide is an important step preceding the formation of compact myelin.