Compartmentalization, processing and redistribution of the plasma membrane protein CE9 on rodent spermatozoa: Relationship of the annulus to domain boundaries in the plasma membrane of the tail

Abstract

Western blotting, immunofluorescence and immunogold electron microscopy were used to examine the compartmentalization, processing and redistribution of the integral plasma membrane protein CE9 on the spermatozoa of rats, mice and hamsters. In each species examined, spermatozoal CE9 was found to undergo endoproteolytic processing followed by a net redistribution from the posterior-tail domain into the anterior-tail domain of the plasma membrane during epididymal maturation. Compared to spermatozoa of the rat and mouse, those of the hamster were found to express a greater proportion of their CE9 within the anterior-tail plasma membrane domain at all stages of maturation. As a consequence, CE9 was judged to be a suitable marker for two different spermatozoal plasma membrane domains: the posterior-tail plasma membrane domain (spermatozoa from the testis and caput epididymidis of the rat and mouse) and the anterior-tail domain (spermatozoa from the cauda epididymidis of the hamster). Immunogold electron microscopy was used to pinpoint the positions of the boundaries of these CE9-containing plasma membrane domains at a high level of resolution. In each case, the position of the CE9 domain boundary was found to be strongly correlated with that of the subplasmalemmal electron-dense ring known as the annulus. The precise spatial relationship between the CE9 domain boundary and the annulus was, however, found to differ significantly among species and/or as a function of maturation.

Validating Missing Proteins in Human Sperm Cells by Targeted Mass-Spectrometry- and Antibody-based Methods

“…This peculiar staining corresponds to the Annulus , a structure located beneath the plasma membrane that connects the midpiece and the principal piece of mature sperm flagellum (for a review, see ref ). Its biogenesis and functional significance remain unclear, but the Annulus might behave as a morphological organizer, guiding flagellum assembly and preventing caudal displacement of mitochondria during spermiogenesis, , and as a diffusion barrier, confining proteins to particular compartments of the mature sperm tail . Interestingly, only a few proteins have been shown to date to localize to the Annulus in the mouse and human (for a review, see ref ).…”

“…Its biogenesis and functional significance remain unclear, but the Annulus might behave as a morphological organizer, guiding flagellum assembly and preventing caudal displacement of mitochondria during spermiogenesis, 56,57 and as a diffusion barrier, confining proteins to particular compartments of the mature sperm tail. 58 Interestingly, only a few proteins have been shown to date to localize to the Annulus in the mouse and human (for a review, see ref 55). C14orf177 immunoreactivity was also observed in the midpiece of ejaculated sperm (Figure 3D).…”

The involvement of immunoglobulin superfamily proteins in spermatogenesis and sperm-egg interaction

“…Sertoli cells express an IgSF protein, nectin-2/CD155, that is grouped in the class of cell adhesion molecules. [1][2][3] Germ cells express a number of IgSF proteins including basigin, [4][5][6][7][8] CE9, [9][10][11] MC31, [12][13][14] IgSF4, 15 RA175, 16,17 SG-IGSF, 18,19 Nectin-3, 2 IgSF11, 20 Ly9/CD150, 21 JAM-C, 22 nectin-like molecule-2 (necl-2), 23 and BT-IgSF. 24 Mouse basigin is homologous to rat CE9 and MC31.…”