Developmentally regulated markers in the postnatal cervical spinal cord of the opossum Monodelphis domestica.

The aim of this study was to identify developmentally regulated immunocytochemical markers to assess development in the cervical spinal cord of Monodelphis domestica. We demonstrate that two commercially available antibodies exhibit altered patterns of distribution during early postnatal development. Although neurofilament staining was present at birth, only the phosphorylated form, recognised by monoclonal antibodies 2F11 or SMI31 could be detected. Non-phosphorylated neurofilament, recognised by monoclonal antibody SMI32, only became detectable around postnatal day 4 (P4) but was restricted to cells in the ventral horn until 5 weeks postnatum. By 7.5 weeks, SMI32 immunoreactivity (IR) was found throughout the grey matter in a pattern similar to that in the adult for both SMI32 and microtubule-associated protein 2 (MAP2). The intermediate filament proteins, glial fibrillary acidic protein (GFAP) and vimentin (VIM), were detectable at birth in radially oriented, fibrous cells, but GFAP-IR was restricted to the ventral half of the cord. This ventral to dorsal gradient of GFAP-IR diminished during the first week of postnatal life, disappearing by P8. Many astrocyte-like, GFAP-positive cells were clearly present by 38 days and, in the adult, were abundant in the white matter. A few VIM-IR cells remained in the adult cord, also within the white matter. We suggest that SMI32 and GFAP are useful, developmentally regulated markers for studies of opossum spinal cord development. We are currently using these markers to investigate the pronounced rostral to caudal gradient in the postnatal spinal cord and to assess development in the cultured spinal cord.

Oligodendrocyte development and differentiation in the rumpshaker mutation.

The jimpy rumpshaker (jprsh) mutation is an amino acid substitution in exon 4 (Ile186-->Thr) of the proteolipid protein (PLP) gene on the X chromosome. Affected mice show moderate hypomyelination of the central nervous system (CNS) with increased numbers of oligodendrocytes in the white matter of the spinal cord, a feature distinguishing them from other PLP mutations such as jp, in which premature cell death occurs with reduced numbers of oligodendrocytes. Myelin sheaths of jprsh immunostain for myelin basic protein (MBP) and DM-20, but very few contain PLP. This study examines the differentiation of oligodendrocytes cultured from the spinal cords of young mutant and wild type mice using various surface and cytoplasmic antigenic markers to define the stage of development. The majority of oligodendrocytes from mutant mice progress normally to express MBP; approximately 30%, relative to wild type, contain DM-20 at the in vivo age of 16 days, but very few immunostain for PLP or the O10 and O11 markers. The morphology of mutant cells in respect to membrane sheets and processes appears similar to normal. The jprsh oligodendrocyte is, therefore, characterized by a failure to express the markers indicative of the most mature cell; however, it is probably able to achieve a normal period of survival. These data, taken in conjunction with previous results, suggest that the PLP gene has at least two functions; one, probably involving PLP, is concerned with a structural role in normal myelin compaction; the other, perhaps related to DM-20 (or another lower molecular weight proteolipid), is essential for cell survival. The mutation in jprsh at residue 186 suggests that this region, which is common to PLP and DM-20, is not critical for this latter function.