Department of Molecular Biology
University of Wyoming
Laramie, WY 82071-3944
THE ROLE OF FORKED PROTEINS IN ACTIN FIBER BUNDLE CONSTRUCTION
Actin binding proteins are involved in creating and regulating the different kinds of actin structures in the cell, which determine cell shape and movement. The forked proteins are a new type of actin binding protein which are required for the construction of very long (300 mm) actin fiber bundles during bristle development in Drosophila. These fiber bundles are morphologically very similar to actin fiber bundles present in vertebrate intestinal brush border and in stereocilia in the ear and kidney, but much larger. The forked gene encodes six proteins, with overlapping coding regions, which differ primarily in their amino-terminal ends (Hoover et al. Genetics 135;507, 1993). The forked proteins are actin binding proteins which are homologous to the vertebrate actin binding proteins, the espins. These were originally identified in rat testis ectoplasmic specializations but have now been also found in kidney and intestinal microvilli and in ear stereocilia, reviewed by Bartles, Curr. Opin. Cell Biol. 12;72, 2000. We are studying the role(s) of forked proteins in actin fiber bundle formation in Drosophila bristles and in vertebrate cell lines. We have shown that forked proteins are synthesized and concentrated in bristle tips just prior to the formation of actin bundles, and that they can induce actin bundle formation in transiently transfected vertebrate cells. This suggests that they play a critical role in initiating bundle formation. We plan to use the transfection of vertebrate cells to further define the essential parts of the protein required for bundle formation and to use affinity chromatography and the yeast two-hybrid system to identify the regions of forked which interact with other proteins. P-factor transformation with forked genes mutated in these regions will then be used to clarify the roles of each in actin bundle formation in bristles. A better understanding of the roles played by forked in the construction and maintenance of these actin bundles should provide in formation useful for human health possibly including enhancing hearing and improving kidney and small intestine function.
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