Migration of the guinea pig sperm membrane protein PH-20 from one localized surface domain to another does not occur by a simple diffusion-trapping mechanism.
The redistribution of membrane proteins on the surface of cells is a prevalent feature of differentiation in a variety of cells. In most cases the mechanism responsible for such redistribution is poorly understood. Two potential mechanisms for the redistribution of surface proteins are: (1) passive diffusion coupled with trapping, and (2) active translocation. We have studied the process of membrane protein redistribution for the PH-20 protein of guinea pig sperm, a surface protein required for sperm binding to the egg zona pellucida (P. Primakoff, H. Hyatt, and D. G. Myles (1985). J. Cell Biol. 101, 2239-2244). PH-20 protein is localized to the posterior head plasma menbrane of the mature sperm cell. Following the exocytotic acrosome reaction, PH-20 protein moves into the newly incorporated inner acrosomal membrane (IAM), placing it in a position favorable for a role in binding sperm to the egg zona pellucida (D. G. Myles, and P. Primakoff (1984), J. Cell Biol. 99, 1634-1641). To analyze the mechanistic basis for this protein migration, we have used fluorescence microscopy and digital image processing to characterize PH-20 protein migration in individual cells. PH-20 protein was observed to move against a concentration gradient in the posterior head plasma membrane. This result argues strongly against a model of passive diffusion followed by trapping in the IAM, and instead suggests that an active process serves to concentrate PH-20 protein toward the boundary separating the posterior head and IAM regions. A transient gradient of PH-20 concentration observed in the IAM suggests that once PH-20 protein reaches the IAM, it is freely diffusing. Additionally, we observed that migration of PH-20 protein was calcium dependent.
Cowan
A E
AE
Department of Physiology, University of Connecticut Health Center, Farmington 06032.
Myles
D G
DG
Koppel
D E
DE
D000177:Acrosome / Q000648:ultrastructure*; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000648:ultrastructure; D004058:Diffusion; D005089:Exocytosis; D006168:Guinea Pigs; D006821:Hyaluronoglucosaminidase; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D013094:Spermatozoa / Q000502:physiology / Q000648:ultrastructure*
D015815:Cell Adhesion Molecules; D008565:Membrane Proteins; D000001:Calcimycin; D006821:Hyaluronoglucosaminidase; C066852:hyaluronidase PH-20; D002118:Calcium