Type X: Prenylation-defective human connexin32 mutants are normally localized an

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J Neurosci. 2005 Aug 3;25(31):7111-20.

Prenylation-defective human connexin32 mutants are normally localized

and function equivalently to wild-type connexin32 in myelinating

Schwann cells.

Huang Y, Sirkowski EE, Stickney JT, Scherer SS.

Department of Neurology, The University of Pennsylvania Medical

Center, Philadelphia, Pennsylvania 19104, USA.

Mutations in GJB1, the gene encoding the gap junction protein

connexin32 (Cx32), cause the X-linked form of Charcot-Marie-Tooth

disease, an inherited demyelinating neuropathy. The C terminus of

human Cx32 contains a putative prenylation motif that is conserved in

Cx32 orthologs. Using [3H]mevalonolactone ([3H]MVA) incorporation, we

demonstrated that wild-type human connexin32 can be prenylated in

COS7 cells, in contrast to disease-associated mutations that are

predicted to disrupt the prenylation motif. We generated transgenic

mice that express these mutants in myelinating Schwann cells. Male

mice expressing a transgene were crossed with female Gjb1-null mice;

the male offspring were all Gjb1-null, and one-half were transgene

positive; in these mice, all Cx32 was derived from expression of the

transgene. The mutant human protein was properly localized in

myelinating Schwann cells in multiple transgenic lines and did not

alter the localization of other components of paranodes and

incisures. Finally, both the C280G and the S281x mutants appeared

to " rescue " the phenotype of Gjb1-null mice, because transgene-

positive male mice had significantly fewer abnormally myelinated

axons than did their transgene-negative male littermates. These

results indicate that Cx32 is prenylated, but that prenylation is not

required for proper trafficking of Cx32 and perhaps not even for

certain aspects of its function, in myelinating Schwann cells.