Expression and Localization of Caveolin-1, and the Presence of Membrane Rafts, in Mouse and Guinea Pig Spermatozoa

Abstract

In somatic cells, caveolin-1 plays several roles in membrane dynamics, including organization of detergent-insoluble lipid rafts, trafficking of cholesterol, and anchoring of signaling molecules. Events in sperm capacitation and fertilization require similar cellular functions, suggesting a possible role for caveolin-1 in spermatozoa. Immunoblot analysis demonstrated that caveolin-1 was indeed present in developing mouse male germ cells and both mouse and guinea pig spermatozoa. In mature spermatozoa, caveolin-1 was enriched in a Triton X-100-insoluble membrane fraction, as well as in membrane subdomains separable by means of their light buoyant densities through sucrose density gradient centrifugation. These data indicated the presence of membrane rafts enriched in caveolin-1 in spermatozoa. Indirect immunofluorescence analysis revealed caveolin-1 in the regions of the acrosome and flagellum in sperm of both species. Confocal immunofluorescence analysis of developing mouse male germ cells demonstrated partial co-localization with a marker for the acrosome. Furthermore, syntaxin-2, a protein involved in acrosomal exocytosis, was present in both raft and nonraft fractions in mature sperm. Together, these data indicated that sperm membranes possess distinct raft subdomains, and that caveolin-1 localized to regions appropriate for involvement with acrosomal biogenesis and exocytosis, as well as signaling pathways regulating such processes as capacitation and flagellar motility.

A soluble adenylyl cyclase from sea urchin spermatozoa

“…Speract from the egg jelly of S. purpuratus activates GC [4 9, 50 ] (reviewed in [5,51]). In contrast to mouse and guinea pig sperm [42], SU sperm microdomains do not contain the caveolae marker caveolin (a 21-24 kDa integral membrane protein), although caveolin is present in the whole sperm lysate. As the speract receptor, a GPI-anchored protein and G sα coimmunoprecipitated together, Ohta et al, [52] suggested that this LD-DIM could constitute a signaling complex involved in regulating sperm respiration, motility and the acrosome reaction (AR) [52].…”

“…Sea urchin sperm membrane microdomains are physiologically functional [34], as has been shown in mammals [41][42][43][44] and the ascidian Ciona intestinalis [45]. Both SUsAC and tmACs, have been found associated with membrane microdomains (reviewed in [46,47]).…”

Ca2+-dependent Localization of Integrin-linked Kinase to Cell Junctions in Differentiating Keratinocytes

“…Similarly, we used Na ϩ /K ϩ ATPase as a marker for Triton X-100-soluble proteins (26) and found that it was exclusively present in this fraction. We also probed the membranes with ␣-actinin and caveolin 1, which are two proteins that generally segregate to Triton X-100-insoluble fractions (27,28). We found that caveolin 1 was present exclusively in the Triton X-100-insoluble portion of extracts from both undifferentiated and differentiated keratinocytes.…”

Sperm head membrane reorganisation during capacitation

“…A few marker proteins were described for lipid rafts: caveolin which is a cholesterol interacting protein involved in clathrin independent endocytosis of caveolae (Elliott et al, 2003;Nabi and Le, 2003) and flotillin, whose function is not yet completely understood, although it has a prohibitin homology (PHB) domain that is supposed to interact with the raft by constituting a primordial lipid recognition motif (Morrow and Parton, 2005). Both caveolin and flotillin are present in mammalian sperm (Travis et al, 2001;Cross, 2004;Sleight et al, 2005). In porcine sperm, both proteins were detected in the plasma membrane over the acrosome in a dispersed, punctuated pattern (van Gestel et al, 2005a).…”