Organization of planar rafts, caveolae and steroid receptors on spermatozoa during development

Sperm membranes undergo progressive structural and functional modifications during epididymal maturation, capacitation and acrosome reaction. Though sperm membranes have raft microdomains, our understanding on the reorganization of membrane rafts during these events is limited. Using caveolin1 (CAV1) and ganglioside GM-1 as markers of membrane rafts, we studied the organization of sperm membrane rafts during epididymal maturation, in vitro capacitation and progesterone-induced acrosome reaction. We also evaluated the effect of raft disruption by methyl beta cyclodextrin on sperm hyperactivation, progesterone induced acrosome reaction and sperm-zona pellucida binding in vitro. CAV1 and ganglioside GM-1 showed transient non-overlapping localization pattern on sperm head during the intermediate phase of epididymal maturation and ended with co-localization on the acrosomal region toward the advanced stages of epididymal maturation and subsequent capacitation. CAV1 was excluded from sperm membrane rafts during capacitation and acrosome reaction. Progesterone receptor (PR) was present in the caveolar rafts of spermatozoa from testis, caput epididymidis and corpus epididymidis, but was not detected in that from cauda epididymidis. Further, capacitation was associated with the appearance of PR in non-caveolar rafts. Estrogen receptors ERα and ERβ, which were located in the caveolar rafts of spermatozoa from testis and epididymides, appeared in the non-caveolar rafts during capacitation and acrosome reaction. It appears that PR, ERα and ERβ were sequestered in the caveolar rafts of spermatozoa during epididymal maturation, and the exit of CAV1 from the membrane rafts overlying the acrosome during capacitation might free them from the sequestration that might trigger PR into action.