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

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 of 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.