Epididymosomes are involved in the acquisition of new sperm proteins during epididymal transit

Abstract

During epididymal transit, spermatozoa acquire new proteins. Some of these newly acquired proteins behave as integral membrane proteins, including glycosylphosphatidylinositol (GPI)-anchored proteins. This suggests that the secreted epididymal proteins are transferred to spermatozoa by an unusual mechanism. Within the epididymal lumen, spermatozoa interact with small membranous vesicles named epididymosomes. Many proteins are associated with epididymosomes and the protein composition of these vesicles varies along the excurrent duct and differs from soluble intraluminal proteins. Some epididymosome-associated proteins have been identified and their functions in sperm maturation hypothesized. These include P25b, a zona pellucida binding protein, macrophage migration inhibitory factor, enzymes of the polyol pathway, HE5/CD52, type 5 glutathione peroxidase, and SPAM1 or PH-20. The electrophoretic patterns of proteins associated to epididymosomes are complex and some of these proteins are transferred to defined surface domains of epididymal spermatozoa. Epididymosomes collected from different epididymal segments interact differently with spermatozoa. This protein transfer from epididymosomes to spermatozoa is time-dependent, temperature-dependent and pH-dependent, and is more efficient in the presence of zinc. Some proteins are segregated to lipid raft domains of epididymosomes and are selectively transferred to raft domains of the sperm plasma membrane. Some evidence is presented showing that epididymosomes are secreted in an apocrine manner by the epididymal epithelial cells. In conclusion, epididymosomes are small membranous vesicles secreted in an apocrine manner in the intraluminal compartment of the epididymis and play a major role in the acquisition of new proteins by the maturing spermatozoa.

Cysteine‐rich secretory proteins are not exclusively expressed in the male reproductive tract

“…Within the corpus epididymis, the staining of epididymosomes was also evident consistent with a recent proteomic analysis of human epididymosomes (Thimon et al, 2008). Epididymosomes are transport vesicles involved in the transfer of epididymal proteins onto sperm (Sullivan et al, 2007). In accordance with the mRNA expression reported by Nolan et al (2006), CRISP1 staining intensity increased in a proximal to distal direction (Fig.…”

Interpreting histopathology in the epididymis

“…12 In the past 3 decades it has been shown that small membranous vesicles secreted by epididymal epithelial cells, i.e., epididymosomes, are involved in this sperm maturation. [13][14][15] Interestingly these epididymosomes have also been shown to transfer a specific sperm binding protein (ELSPBP1) to dead sperm during transit. 16 Recently, it was suggested that the cytoplasmic droplets, which are small cytoplasmic residues attached to the sperm after their release fromthe germinal epithelium and which migrates caudally along the sperm during epididymal transit, 13 represent a transient organelle that serves as an energy source essential for epididymal sperm maturation.…”

Sperm head membrane reorganisation during capacitation

“…Both proteins have a restricted distribution in the anterior tip of the sperm head surface (i.e. the area involved in initial sperm-zona binding) (Petrunkina et al, 2003;Ensslin et al, 1998) Likewise, it has been recently demonstrated that many GPI anchored proteins, which are highly exclusive for the DRM, and thus considered to be specific for lipid rafts (for review see Hooper, 1999), are acquired by the surface of the maturing sperm cell by epididymosomes (Sullivan et al, 2007). Epididymsomes are apocrine-secreted, tiny membraneous vesicles, also called exosomes, that originate from the epithelium of the epididymal tract (Frenette and Sullivan, 2001;Hermo and Jacks, 2002).…”