Expression of myelin proteins in the opossum optic nerve: Late appearance of inhibitors implicates an earlier non-myelin factor in preventing ganglion cell regeneration

Abstract

The pattern of appearance of myelin-associated proteins in the visual system of the Brazilian opossum Monodelphis domestica is described. Whole mounts of optic nerve, chiasm, and optic tract were sectioned horizontally and incubated with antibodies to myelin basic protein (MBP), proteolipid protein (PLP), myelin-associated glycoprotein (MAG), "Rip," and the neurite inhibitory protein (IN-1), followed by visualization with diaminobenzidine and a peroxidase-conjugated secondary antibody. PLP is first detectable 24 days after birth (P24) at the centre of the optic chiasm. MBP, MAG, Rip, and IN-1 appear first in the same area at P26. By P28 the distribution of all proteins is similar, occupying the entire chiasm, optic tracts, and prechiasmatic portion of the optic nerves. Protein expression progresses along the optic nerve to reach the lamina cribrosa by P34, coincident with the time of eye opening. A critical period in which the retinofugal pathway has a regenerative capacity has recently been observed in Monodelphis. This period ends at P12, 2 weeks before the appearance of the myelin-associated inhibitory proteins MAG and IN-1. These results therefore suggest that regeneration in the developing retinofugal projection of the opossum is restricted by an earlier non-myelin factor, which is in contrast to current literature on the spinal cord.

Age-dependent failure of axon regeneration in organotypic culture of gerbil auditory midbrain

“…This result is in accordance with previous studies showing a transient period for axonal outgrowth across a lesion site (Kalil and Reh, 1982;Xu and Martin, 1989;Shimizu et al, 1990;Hasan et al, 1993;Li et al, 1995;MacLaren and Taylor, 1995;Dusart et al, 1997), a period that coincides with limited myelination (Jhaveri et al, 1992;Keirstead et al, 1992;Ghooray and Martin, 1993;Kapfhammer and Schwab, 1994;Varga et al, 1995;MacLaren, 1996). These experiments suggest that failure to regenerate is due to growth-inhibitory molecules on myelin, or molecules that are strongly adhesive and which prevent axons from rapid growth.…”

Exposure to As, Cd and Pb-mixture impairs myelin and axon development in rat brain, optic nerve and retina

“…The expression of the myelin and axon proteins progresses along the O.N. to reach the lamina cribrosa, which coincides with the eye opening (MacLaren, 1996). Therefore, the MM-mediated delay in eye opening could well correlate with the TEM and protein data.…”

A glial palisade delineates the ipsilateral optic projection in Monodelphis

“…There are a multitude of molecular markers at this location (Stretavan, 1993;Marcus et al, 1995) and it is difficult to isolate their role as being specifically for the recognition of ipsilaterally projecting ganglion cells. These molecules may have other unrelated roles specific to midline structures in general (Mori et al, 1990;Snow et al, 1990;Ghooray & Martin, 1993), or reflect nonspecific maturational factors, for instance, myelination, which starts at the chiasmatic midline in this species (MacLaren, 1996b). In this report, it is shown at the cellular level that a discrete subpopulation of glial cells exists at the point of segregation of the ipsilateral pathway well away from the chiasmatic midline.…”