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Department of Cell Biology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven,
Connecticut 06510
Amphiphysin (amphiphysin I), a dominant
autoantigen in paraneoplastic Stiff-man syndrome, is a
neuronal protein highly concentrated in nerve terminals, where it has a putative role in endocytosis. The
yeast homologue of amphiphysin, Rvs167, has pleiotropic functions, including a role in endocytosis and in actin dynamics, suggesting that amphiphysin may also be
implicated in the function of the presynaptic actin cytoskeleton. We report here the characterization of a
second mammalian amphiphysin gene, amphiphysin II
(SH3P9; BIN1), which encodes products primarily expressed in skeletal muscle and brain, as differentially
spliced isoforms. In skeletal muscle, amphiphysin II is
concentrated around T tubules, while in brain it is concentrated in the cytomatrix beneath the plasmamembrane of axon initial segments and nodes of Ranvier. In
both these locations, amphiphysin II is colocalized with
splice variants of ankyrin3 (ankyrinG), a component of
the actin cytomatrix. In the same regions, the presence
of clathrin has been reported. These findings support the hypothesis that, even in mammalian cells, amphiphysin/Rvs family members have a role both in endocytosis and in actin function and suggest that distinct amphiphysin isoforms contribute to define distinct
domains of the cortical cytoplasm. Since amphiphysin II (BIN1) was reported to interact with Myc, it may also
be implicated in a signaling pathway linking the cortical
cytoplasm to nuclear function.
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