Plasmolipin: genomic structure, chromosomal localization, protein
expression pattern, and putative association with
* Ulrich Pippirs,
* Angelika Ko¨hler,
Hans Werner Mu¨ller,
Department of Molecular Neurobiology, Neurology, Heinrich-Heine-University, Moorenstrasse 5, 40225 Du¨sseldorf, Germany
Institute of Human Genetics, Justus-Liebig-University, Schlangenzahl 14, 35392 Giessen, Germany
Received: 19 April 2001 / Accepted: 23 July 2001
Abstract. Plasmolipin is a membrane protein and belongs to the
tetraspan molecule (4TM) family, an expanding group of myelin
proteins many of which could be linked to human hereditary de-
myelinating neuropathies. We have cloned and sequenced the
mouse plasmolipin gene, revealing the common organization of
the 4TM gene group with four exons and a large first intron.
Western blot analysis with an antibody raised against the C-
terminal intracellular part of the protein showed that plasmolipin is
expressed not only in the nervous system and kidney, but also in
a number of other tissues such as thymus, testis, lung, and thyroid
gland. By means of radiation hybrid mapping and FISH analysis,
we could localize the human plasmolipin gene to Chromosome
16q13 within the putative region of the Bardet-Biedl syndrome
type 2 (BBS2) gene locus. BBS2 is a clinically and genetically
heterogeneous group of disorders resulting in rod-cone dystrophy,
obesity, postaxial polydactyly, renal dysfunction, and mental re-
tardation, which were very recently associated with a novel gene
designated BBS2. With respect to intrafamiliar variations in the
manifestation of BBS, we suggest that plasmolipin might be either
another candidate gene or a modifier of the BBS2 phenotype.
Plasmolipin was initially isolated from kidney plasma membranes
as a protein of 20 kDa (Tosteson and Sapirstein 1981) and classi-
fied as a proteolipid (Lees et al. 1979) owing to its high proportion
of hydrophobic amino acids and its solubility in organic solvents.
Subsequent Northern blot analysis detected plasmolipin ex-
pression in Schwann cells of sciatic nerves and oligodendrocytes
in brain (Cochary et al. 1990; Fischer et al. 1991). Developmental
analysis indicated a strong temporal correlation between plasmo-
lipin mRNA-expression and postnatal myelination in the periph-
eral and central nervous system, as well as remyelination during
sciatic nerve regeneration (Gillen et al. 1996). Furthermore, topo-
graphic models based on the nucleotide sequence predict four pu-
tative transmembrane regions (Gillen et al. 1996), a cardinal fea-
ture of the tetraspan molecule family, an expanding group of my-
elin proteins including proteolipid protein (PLP; Milner et al.
1985), peripheral myelin protein 22 kDa (PMP22; Spreyer et al.
1991) and myelin and lymphocyte protein (MAL; Schaeren-
Wiemers et al. 1995). Most of them have been shown to be in-
volved in causing hereditary demyelinating neuropathies like
PMP22 in Charcot-Marie-Tooth 1A (for review see Mu¨ller 2000)
and PLP in Pelizaeus-Merzbacher disease (Hudson et al. 1989).
Unfortunately, little is known about the biological function of
plasmolipin in vivo and its potential relation to neurological dis-
In the present investigation, we have determined the genomic
structure, protein expression pattern, and chromosomal localiza-
tion of plasmolipin. Surprisingly, we detected the plasmolipin gene
near the chromosomal locus of the Bardet-Biedl syndrome (BBS,
MIM 209900). BBS is a generic description for a clinically and
genetically heterogeneous group of disorders resulting in rod-cone
dystrophy, obesity, postaxial polydactyly, hypogenitalism, renal
dysfunction, and mental retardation (Bardet 1995; Biedl 1995;
Green et al. 1989; Harnett et al. 1988). Because of this widespread
spectrum of features overlapping with those of the Laurence-Moon
syndrome (additional spastic paraplegia, rare polydactyly) a new
description label, polydactyly-obesity-kidney-eye syndrome, was
proposed recently (Beales et al. 1999).
Interestingly, not every BBS patient shows all known symp-
toms, and within affected families the symptoms may vary (Green
et al. 1989; Beales et al. 2000). Nearly all suffer from rod-cone
dystrophy (approx. 90%), but only approx. 70% have postaxial
polydactyly, and fewer reveal developmental delay (approx. 50%)
or ataxia (approx. 40%; Beales et al. 1999). BBS is linked to at
least six chromosomal loci: BBS1 to Chromosome (Chr) 11q13
(Leppert et al. 1994); BBS2 to Chr 16q13–21 with the gene order
cen–D16S408–2cM–BBS2–5cM–D16S400 (Kwitek-Black et al.
1993); BBS3 to Chr 3p13 (Sheffield et al. 1994); BBS4 to Chr
15q23 (Carmi et al. 1995); BBS5 to Chr 2q31 (Young et al. 1999);
and BBS6 to Chr 20p12 (Katsanis et al. 2000; Slavotinek et al.
Thus far, BBS6 could be linked to a distinct gene, namely the
McKusick-Kaufman syndrome gene (MKKS gene; Katsanis et al.
2000; Stone et al. 2000; Slavotinek et al. 2000), while most other
candidate genes for other BBS types could not be verified up to
now. In general, some authors suggest chaperonins may be in-
volved in causing this syndrome (Slavotinek et al. 2000), molecu-
lar pathways that could be influenced by the genomic background
(Riise et al. 1997) or epistatic interactions between BBS genes
leading to abnormal precursor cell growth or altered differentiation
(Beales et al. 2000).
Materials and methods
Screening of a genomic mouse library.
The genomic mouse 129/
SvevTACfBr P1 library RPCI 21 (414750 clones, average insert size 146.6
kb), constructed at the Roswell Park Cancer Institute by Osoegawa and de
Jong, was provided by the Ressourcen Zentrum/Prima¨r Datenbank (RZPD)
of the German Human Genome Project. Filters were prehybridized in
Church-buffer (7% SDS, 0.5
sodium phosphate pH 7.2) at 68°C for 1 h.
A rat plasmolipin cDNA spanning from nucleotides 372 to 1476 was
labeled with [␣
P]dCTP by using Ready-To-Go DNA Labeling Beads
(Pharmacia). Hybridization was carried out in Church-buffer at 68°C over-
night. Filters were washed twice in 0.1% SDS, 40 m
(pH 7.2) at 25°C for 5 min, and two times at 68°C for 30 min. Autora-
*These authors contribute equally to the work
Correspondence to: F. Bosse; E-mail: email@example.com
Mammalian Genome 12, 933–937 (2001).
© Springer-Verlag New York Inc. 2001