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Updated: May 20, 2026
10:23
Analysis of Epididymal Protein Synthesis and Secretion
Published on: August 25, 2018
Rab27 and Rab3 sequentially regulate human sperm dense-core granule exocytosis
Matías A Bustos1, Ornella Lucchesi, María C Ruete
1Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina.
Summary
Rab27 and Rab3A proteins are crucial for sperm exocytosis, known as the acrosome reaction. This study reveals a Rab-GEF cascade involving Rab27 and Rab3A in dense-core vesicle release.
Area of Science:
- Cell Biology
- Reproductive Biology
- Molecular Biology
Background:
- Secretory Rabs, specifically Rab3 and Rab27, are known regulators of dense-core vesicle exocytosis in neuroendocrine cells.
- Sperm utilize regulated exocytosis, the acrosome reaction, to release their dense-core granule during fertilization.
- Sperm exocytosis shares machinery with neuronal cells but requires active Rab3.
Purpose of the Study:
- To investigate the role of Rab27 in the sperm acrosome reaction.
- To elucidate the interplay between Rab27 and Rab3A in sperm exocytosis.
- To establish a method for detecting GTP-bound forms of Rab3A and Rab27 in human sperm.
Main Methods:
- Utilized streptolysin O-permeabilized human sperm loaded with inhibitory anti-Rab27 antibodies or Rab27-GTP binding domain.
- Developed a fluorescence microscopy technique to detect endogenous Rab3A-GTP and Rab27-GTP in the acrosomal region.
- Introduced recombinant Rab27A loaded with GTP-γ-S and recombinant Rab3A into sperm.
Main Results:
- Rab27 is essential for the acrosome reaction, as its inhibition prevents exocytosis.
- GTP-bound Rab27 and Rab3A levels increase upon initiation of sperm exocytosis.
- Rab27A-GTP was found to recruit Rab3 GDP/GTP exchange factor (GEF) activity, while Rab3A did not affect Rab27-GTP levels.
Conclusions:
- Rab27 plays a critical role in sperm acrosome reaction, alongside Rab3A.
- A novel Rab-GEF cascade, Rab27/Rab3A, is proposed to regulate dense-core vesicle exocytosis.
- Findings highlight a conserved and specific mechanism for sperm exocytosis regulation.
Related Concept Videos
01:25Rab Cascades
Rab GTPases act in a regulated cascade during membrane fusion, helping the lipid bilayers mix. The Rab family of proteins are active when bound to GTP, and inactive when bound to GDP. Hence, they act as guanine nucleotide-dependent molecular switches. Rab-GTP recognizes and binds to long or short-range tethering proteins to capture the target vesicle. These tethers coordinate with SNAREs on the vesicle and the target membrane to assemble the trans SNARE complex that locks the mixing bilayers.
01:14Rab Proteins
Rab proteins constitute the largest family of monomeric GTPases, of which 70 members are present in humans. Rab proteins and their effectors regulate consecutive stages of vesicle transport such as vesicle transport, docking, and fusion to the correct recipient membrane.
Rab proteins switch between a cytosolic, GDP-bound inactive state and a membrane-anchored, GTP-bound active state. By themselves, Rabs show slow rates of GDP/GTP exchange and GTP hydrolysis. Thus, Rab proteins are considered...
Rab proteins switch between a cytosolic, GDP-bound inactive state and a membrane-anchored, GTP-bound active state. By themselves, Rabs show slow rates of GDP/GTP exchange and GTP hydrolysis. Thus, Rab proteins are considered...
01:43SNAREs and Membrane Fusion
Once a transport vesicle has recognized its target organelle, the vesicular membrane needs to fuse with the target membrane to unload the cargo. Transmembrane proteins called SNAREs present on organelle membranes and their vesicles, mediate vesicle fusion.
SNAREs exist in pairs that symmetrically interact and catalyze the fusion of the lipid bilayers in vesicle and target organelle. v-SNARE in the vesicle membrane are single polypeptide chains that bind to a complementary t-SNARE, composed of 2...
SNAREs exist in pairs that symmetrically interact and catalyze the fusion of the lipid bilayers in vesicle and target organelle. v-SNARE in the vesicle membrane are single polypeptide chains that bind to a complementary t-SNARE, composed of 2...
01:33Overview of Secretory Vesicles
Secretory vesicles, also known as dense core vesicles (DCVs), are membrane-bound vesicles that transport secretory proteins, such as hormones or neurotransmitters. Regulated secretory vesicles transport proteins from the trans-Golgi network to the exterior of the cell. Proteins present in regulated secretory vesicles are required to be rapidly exocytosed in large amounts upon a specific stimulus.
Various proteins regulate the aggregation of molecules inside the secretory vesicles. Chromogranins...
Various proteins regulate the aggregation of molecules inside the secretory vesicles. Chromogranins...
01:33Coat Assembly and GTPases
Vesicles incorporate different coat protein subunits in different cell locations, which changes the properties of the coat, such as the shape and geometry of the transport vesicles. Thus, vesicle coat proteins also play a significant role in cargo selection.
Coat assembly depends on the local availability of phosphatidylinositol phosphates or PIPs and GTP-binding proteins. Adaptor proteins, which link the coat proteins to the membrane, bind to these PIPs and play a crucial role in controlling...
Coat assembly depends on the local availability of phosphatidylinositol phosphates or PIPs and GTP-binding proteins. Adaptor proteins, which link the coat proteins to the membrane, bind to these PIPs and play a crucial role in controlling...
01:41Spermatogenesis
Spermatogenesis is the process by which haploid sperm cells are produced in the male testes. It starts with stem cells located close to the outer rim of seminiferous tubules. These spermatogonial stem cells divide asymmetrically to give rise to additional stem cells (meaning that these structures “self-renew”), as well as sperm progenitors, called spermatocytes. Importantly, this method of asymmetric mitotic division maintains a population of spermatogonial stem cells in the male reproductive...