FER-1 regulates Ca2+-mediated membrane fusion during C. elegans spermatogenesis

Abstract

FER-1 is required for fusion of specialized vesicles, called membranous organelles, with the sperm plasma membrane during Caenorhabditis elegans spermiogenesis. To investigate its role in membranous organelle fusion, we examined ten fer-1 mutations and found that they all cause the same defect in membrane fusion. FER-1 and the ferlin protein family are membrane proteins with four to seven C2 domains. These domains commonly mediate Ca2+-dependent lipid-processing events. Most of the fer-1 mutations fall within these C2 domains, showing that they have distinct, non-redundant functions. We found that membranous organelle fusion requires intracellular Ca2+ and that C2 domain mutations alter Ca2+ sensitivity. This suggests that the C2 domains are involved in Ca2+ sensing and further supports their independent function. Using two immunological approaches we found three FER-1 isoforms, two of which might arise from FER-1 by proteolysis. By both light and electron microscopy, these FER-1 proteins were found to be localized to membranous organelle membranes. Dysferlin, a human homologue of FER-1 involved in muscular dystrophy, is required for vesicle fusion during Ca2+-induced muscle membrane repair. Our results suggest that the ferlin family members share a conserved mechanism to regulate cell-type-specific membrane fusion.

Cytosolic Ca2+ as a multifunctional modulator is required for spermiogenesis inAscaris suum

“…During sperm activation, the sperm specifi c membranous organelle (MO) derived from e ndoplasmic reticulum/Golgi apparatus fuses with the plasma membrane (PM), leaving a permanent invagination on the cell surface and resulting in the exocytosis and translocation of MOs components (Washington and Ward, 2006;Zhao et al, 2012). In fl agellated sperm, Ca 2+ modulates nearly every step of sperm maturation and fertilization including sperm capacitation, hyperactivation, chemotaxis, acrosome reaction and sperm-egg recognition (Breitbart, 2002;Kirichok et al, 2006;Kaupp et al, 2008;Teves et al, 2009).…”

“…However, the role of Ca 2+ in nematode sperm activation was seldom reported. Previously, Ca 2+ was implicated in the regulation of C. elegans sperm activation (Shakes and Ward, 1989;Washington and Ward, 2006). However, the underlying mechanisms remain to be elucidated.…”

“…C. elegans spermatids from the MO fusiondefective mutant fer-1 extend pseudopods in response to the artificial activator (Washington and Ward, 2006), indicating that MO fusion and pseudopod extension are two separate events during sperm activation. Pseudopod extension can be visualized under light microscopy and the fused MOs can be detected as fl uorescent puncta of FM1-43 formed at the rear edge of the cell body (Washington and Ward, 2006;. Our ex vivo time-lapse imaging showed that pseudopod protrusion precedes MO fusion ( Fig.…”

“…Nematode spermatids can be activated in Ca 2+ -free medium (Movie S2) (Ward et al, 1983;Washington and Ward, 2006), indicating that the [Ca 2+ ] i increase might be caused by Ca 2+ release from intracellular store. Ca 2+ oscillations are primarily regulated by IP 3 R (Berridge, 2007), which can be activated by inositol (1,4,5)-trisphosphate (IP 3 ) generated through cleavage of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) by PLC in a variety of cell types (Berridge, 2007).…”

Fertilization and the oocyte-to-embryo transition in C. elegans

“…In hermaphrodites, spermiogenesis occurs in the spermatheca, and in males, it occurs when sperm mixes with seminal fluid during ejaculation into the hermaphrodite during copulation (20). Sperm activation appears to involve cation in-http://bmbreports.org BMB reports flux, pH elevation, and intracellular Ca 2+ release (20)(21)(22)(23)(24). Mature sperm must crawl towards the spermatheca and maintain their position in the reproductive tract while eggs are ovulated into the spermatheca.…”