Composition and expression of spectrin‐based membrane skeletons in non‐erythroid cells

Abstract

Cellular differentiation is often accompanied by the expression of specialized plasma membrane proteins which accumulate in discrete regions. The biogenesis of these specialized membrane domains involves the assembly and co‐localisation of a spectrin‐based membrane skeleton. While the constituents of the membrane skeleton in non‐erythroid cells are often immunologically related to erythroid spectrin, ankyrin, and protein 4.1, there are structural and functional differences between the isoforms of these membrane skeleton polypeptides, as well as highly variable patterns of expression during cellular differentiation. We consider this heterogeneity of structure and expression during development in the context of the hypothesis that non‐erythroid spectrin, ankyrin, and protein 4.1 are involved in the formation of specialized membrane domains.

A beta-spectrin isoform from Drosophila (beta H) is similar in size to vertebrate dystrophin.

“…Variation in the/3 subunlt modulates at least three properties of the spectrin tetramer. In chicken the protein 4.1sensitivity of the spectrin-actin interaction, the interaction with the membrane through ankyrin, and the length of the spectrin tetramer all vary independently of the ot subunit (Coleman et al, 1989;Moon and McMahon, 1987). Here we show that the length of the Drosophila spectrin tetrarner depends on whether it includes a 430-or a 270-kD B subunit (protein 4.1 and ankyrin have not been identified in Drosophila).…”

“…T hE membrane skeleton of eukaryotic cells is made up of a specialized subset of cytoskeletal proteins that contribute to membrane structure and in some cases link the membrane to the transcellular cytoskeleton. Spectrins have been identified at the plasma membrane of many eukaryotic cell types and spectrin molecules can be categorized according to their structure, composition, and distribution (Moon and McMahon, 1987;Coleman et al, 1989). In most cases, the ot and/3 subunits of spectrin associate laterally to form heterodimers that in turn associate head-to-head to form tetramers.…”

Identification of a 33-kilodalton cytoskeletal protein with high affinity for the sodium channel

“…In erythrocytes it has been established that the lateral mobility of the anion transporter is restricted due to its interactions with components of the membrane skeleton [reviewed by Bennett (1985) and Marchesi (1985)]. Closely related analogues of the erythrocyte membrane skeleton proteins spectrin, ankyrin, actin, and protein 4.1 have been identified in nonerythroid tissues [reviewed by Moon and McMahon (1987)], and it seems likely that the cytoskeleton may perform a similar anchoring function in nonerythroid tissues. Koenig and Repasky (1985) have shown by immunofluorescence that spectrin is localized at the nodes of Ranvier and not at paranodal regions in goldfish neurons, suggesting that interaction with the spectrin-based membrane skeleton may play a role in maintaining the specific localization of neuronal proteins.…”