1002 Jacobs, Bongarzone, Campagnoni, and Campagnoni
cells by Northern blot, reverse transcription-polymerase
chain reaction (RT-PCR), and in situ hybridization (3,
15). PCR fragments containing PLP/DM20 exons 3 to 4
have also been identiﬁed in a variety of mouse tissues
including liver, intestine, adipose tissue, lung, muscle,
kidney, and thymus (15). In this report, immunostain-
ing for sr-PLP/DM20 was detected in many of these
same tissues. Currently, it is not clear whether the mRNA
products detected in these studies reﬂect DM20 or
sr-DM20 transcripts. However, the primers used in the
RT-PCR experiments by Nadon et al. (15) would recog-
nize and amplify an equivalent size product from either
In summary, the sr-products of the PLP gene are
expressed throughout the embryo in a variety of cell
types. The widespread pattern of expression during mul-
tiple stages of development supports the notion that
sr-PLP and sr-DM20 serve a function unrelated to mye-
lination. In nearly all cell types that express sr-PLP/
DM20, the proteins have been localized in the cell body.
In oligodendrocytes, sr-PLP/DM20 co-localize with traf-
ﬁcking molecules clathrin and syntaxin 6 suggesting a
possible role of the sr-PLPs in vesicular transport (8).
Whether the sr-PLPs serve a similar function in other
cell types remains to be determined.
The authors wish to thank Dr. Ellen Carpenter and Dr. Robin Fisher
for their helpful discussions during the preparation of this manuscript.
This work was supported by grants from the National Institutes of Health
(NS23022 and NS33091) and from the National Multiple Sclerosis Soci-
ety (RG2693). E. C. J. was supported in part from an National Research
Service Award grant (MH199250304b).
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