The jimpy rumpshaker (jp(rsh)) 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 centr
al nervous system (CNS) with increased numbers of oligodendrocytes in
the white matter of the spinal cord, a feature distinguishing them fro
m other PLP mutations such as jp, in which premature cell death occurs
with reduced numbers of oligodendrocytes. Myelin sheaths of jp(rsh) i
mmunostain for myelin basic protein (MBP) and DM-20, but very few cont
ain PLP. This study examines the differentiation of oligodendrocytes c
ultured 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 pro
gress normally to express MBP; approximately 30%, relative to wild typ
e, contain DM-20 at the in vivo age of 16 days, but very few immunosta
in 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 jp(rsh) oligodendrocyte is, therefore, characterized by a failure
to express the markers indicative of the most mature cell; however, i
t 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, perhap
s related to DM-20 (or another lower molecular weight proteolipid), is
essential for cell survival. The mutation in jp(rsh) at residue 186 s
uggests that this region, which is common to PLP and DM-20, is not cri
tical for this latter function. (C) 1993 Wiley-Liss, Inc.