Spectrin in the leading lamella of cultured chicken fibroblasts.
The leading lamella is a highly dynamic cell compartment of locomoting fibroblasts. Based on its well-characterized internal cytoskeletal architecture, the leading lamella can be divided into three structurally distinct zones. Much less is known about the membrane components of the leading lamella. In this study, we looked at the distribution of spectrin, the major component of the subplasmalemmal membrane skeleton, in the leading lamella and its relation to the subdivision of the lamellar space in cultured fibroblasts. In immunofluorescence microscopy, a general, plasma membrane-associated staining of spectrin was observed especially in the more central regions of detergent-extracted cells. In the leading lamella, spectrin was seen particularly along the lamellar edge and as small protrusions, or nodes, along the lamellar periphery. A weaker staining was observed in the more proximal regions of the lamella. In wet-cleaved cells also, spectrin was observed along the leading edge and in the protrusions of the lamella. In double immunofluorescence microscopy, a close colocalization of spectrin and actin was seen in the lamellar region. In immunoelectron microscopy of whole-mount preparations, spectrin was also found to be in close association with the actin meshwork in the most peripheral zone of the lamella and it was also associated with the actin-containing microspikes. A weaker labeling for spectrin was observed along the filaments in the proximal regions of the lamella. The node-like accumulations of spectrin seen along the lamellar edge were reactive to antibodies raised against talin and paxillin, suggesting that they represent evolving focal adhesions. The results show that spectrin is particularly present along the leading edge of the leading lamella. It is also present in the active protrusion sites of translocating cells, probably representing evolving adhesion sites. The role of spectrin should therefore be considered when studying the mechanisms of events associated with the locomotive behavior of fibroblasts.
Sormunen
R
R
Department of Pathology, University of Oulu, Finland.
Lehto
V P
VP
D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D005347:Fibroblasts / Q000737:chemistry* / Q000648:ultrastructure; D015151:Immunoblotting; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D013049:Spectrin / Q000032:analysis*
D013049:Spectrin