The Journal of Cell Biology, Vol 116, 1291-1300, Copyright © 1992 by The Rockefeller University Press

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Incorporation of protein into spore coats is not cell autonomous in Dictyostelium

CM West and GW Erdos
Department of Anatomy, College of Medicine, University of Florida, Gainesville 32610-0235.

At maturity, the spores of Dictyostelium are suspended in a viscous fluid droplet, with each spore being surrounded by its own spore coat. Certain glycoproteins characteristic of the spore coat are also dissolved in this fluid matrix after the spore coat is formed. To determine whether any proteins of the coat reside in this fluid phase earlier during the process of spore coat assembly, pairs of strains which differed in a spore coat protein carbohydrate marker were mixed and allowed to form spore coats in each other's presence. We reasoned that proteins belonging to an early, soluble, extracellular pool would be incorporated into the spore coats of both strains. To detect trans- incorporation, spores were labeled with a fluorescent antibody against the carbohydrate marker and each spore's fluorescence was analyzed by flow cytometry. Several proteins of both the outer and inner protein layers of the coat appeared to be faithfully and reciprocally trans- incorporated and hence judged to belong to a soluble, assembly-phase pool. Western blot analysis of sorted spores, and EM localization, confirmed this conclusion. In contrast, one outer-layer protein was not trans-incorporated, and was concluded to be insoluble at the time of secretion. Three classes of spore coat proteins can be described: (a) Insoluble from the time of secretion; (b) present in the early, soluble pool but not the late pool after spore coat formation; and (c) present in the soluble pool throughout spore coat assembly. These classes may, respectively: (a) Nucleate spore coat assembly; (b) comprise a scaffold defining the dimensions of the nascent spore coat; and (c) complete the assembly process by intercalation into the scaffold.
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This article has been cited by other articles:

• West, C. M., Nguyen, P., van der Wel, H., Metcalf, T., Sweeney, K. R., Blader, I. J., Erdos, G. W. (2009). Dependence of Stress Resistance on a Spore Coat Heteropolysaccharide in Dictyostelium. Eukaryot Cell 8: 27-36 [Abstract] [Full Text]  
• West, C. M., Zhang, P., McGlynn, A. C., Kaplan, L. (2002). Outside-In Signaling of Cellulose Synthesis by a Spore Coat Protein in Dictyostelium. Eukaryot Cell 1: 281-292 [Abstract] [Full Text]  
• Zhang, Y, Zhang, P, West, C. (1999). A linking function for the cellulose-binding protein SP85 in the spore coat of Dictyostelium discoideum. J. Cell Sci. 112: 4367-4377 [Abstract]  
• Niswonger, M., O'Halloran, T. (1997). Clathrin heavy chain is required for spore cell but not stalk cell differentiation in Dictyostelium discoideum. Development 124: 443-451 [Abstract]  
• Nuckolls, G., Osherov, N, Loomis, W., Spudich, J. (1996). The Dictyostelium dual-specificity kinase splA is essential for spore differentiation. Development 122: 3295-3305 [Abstract]  

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