Chemosensory Ca2+ Dynamics Correlate with Diverse Behavioral Phenotypes in Human Sperm

Abstract

In the female reproductive tract, mammalian sperm undergo a regulated sequence of prefusion changes that "prime" sperm for fertilization. Among the least understood of these complex processes are the molecular mechanisms that underlie sperm guidance by environmental chemical cues. A "hard-wired" Ca 2؉ signaling strategy that orchestrates specific motility patterns according to given functional requirements is an emerging concept for regulation of sperm swimming behavior. The molecular players involved, the spatiotemporal characteristics of such motility-associated Ca 2؉ dynamics, and the relation between a distinct Ca 2؉ signaling pattern and a behavioral sperm phenotype, however, remain largely unclear. Here, we report the functional characterization of two human sperm chemoreceptors. Using complementary molecular, physiological, and behavioral approaches, we comparatively describe sperm Ca 2؉ responses to specific agonists of these novel receptors and bourgeonal, a known sperm chemoattractant. We further show that individual receptor activation induces specific Ca 2؉ signaling patterns with unique spatiotemporal dynamics. These distinct Ca 2؉ dynamics are correlated to a set of stimulus-specific stereotyped behavioral responses that could play vital roles during various stages of prefusion sperm-egg chemical communication.On their journey to locate the oocyte, navigating mammalian sperm depend on both chemical (1) and physical (2, 3) cues to regulate flagellar motion, switch flagellar beat modes, and, thus, direct their movement. How such environmental signals are detected and translated into changes in motility, however, remains largely unknown.Sperm acquire motility upon vaginal deposition (4). This initial swimming behavior is referred to as activated motility and characterized by a relatively low amplitude/high frequency sinusoidal flagellar motion (5). Motile sperm that pass the cervical mucus barrier must locate and enter the oviduct. Only a fraction of sperm present in the uterus (ϳ10% in humans (6)) accomplishes this task. Within the oviductal isthmus, sperm frequently attach to the highly convoluted epithelial surface (3,7,8), forming a sperm reservoir in close proximity to the fertilization site. Upon ovulation, capacitated sperm that adopt a hyperactivated state (i.e. displaying asymmetrical and relatively high amplitude/low frequency flagellar beating) (4), generate sufficient propulsion force to detach from the epithelium, enter the ampulla, and eventually penetrate the cumulus and zona pellucida surrounding the egg (9).Given the small fraction of sperm that reaches the oviduct, a "competitive race" scenario has fallen out of favor in recent years. Instead, effective sperm guidance mechanisms are required to assure a synchronized arrival and encounter of both gametes at the fertilization site (1). Current models propose a complex multistep process of sperm navigation along thermal (2) and chemical (10) gradients. Accordingly, chemical guidance cues are secreted by both the oocyte and the surroundi...

Odorant receptor-mediated sperm activation in disease vector mosquitoes

“…One interpretation of those data is that AgOrs are functional in nonhead tissues in males where they are used in noncanonical chemosensory roles. Given the previous characterizations of functional OR expression in mammalian sperm (23,26,27), we speculated that AgOrs may also contribute functionally to male reproductive tissues in A. gambiae. To address this hypothesis, RNAseq was used to examine relative transcript abundances in A. gambiae testes (Table 1) where more than 30 AgOrs were detected, nine of which had reads per kilobase per million (RPKM) values greater than 1 (Table1) and their percentile ranks ranged between 20 and 45.…”

“…Asterisks indicate significant differences between compound and control buffer samples or between compound with or without VUANT (Mann-Whitney U, P < 0.01). The activation of insect sperm via ionotropic Ors is reminiscent of capacitation of mammalian sperm, which has been linked to signaling pathways mediated by metabotropic ORs (23,26,27) as well as the activity of several ionotropic channels (58,59). These include calcium channels, most notably the sperm cation channels, CatSpers (60)(61)(62)(63), potassium channels such as Kcnu1 (64,65) as well as sodium, proton, bicarbonate, and chloride channels that are localized along the sperm flagella and speculated to act downstream of receptors for diverse extracellular ligands (33,59).…”

“…To explore the possible biological function of AgOrs in A. gambiae testes, and in light of the known responses of vertebrate spermatozoa to exogenous chemical stimuli (23,26,27), we have developed a simple video-based bioassay ( Fig. S4) to examine the amplitudes of flagellar movements of bulk spermatozoa nascent to ruptured testes in response to a range of natural and synthetic compounds.…”

“…Indeed, several studies have suggested the existence of signaling pathways in insect sperm, including proteomics analyses in Aedes aegypti (18) and Drosophila melanogaster (19), although ORs were not identified in those studies. Importantly, OR expression in male germ cells has been reported for numerous mammalian species (20)(21)(22) and evidence for functional expression of ORs in human and mouse sperm have been described (23)(24)(25)(26)(27), although the requirement for human ORs in ligand recognition and fertilization has been seriously challenged (28). In a potentially striking example of convergent evolution, we describe the expression of a subset of ORs in male germ cells of A. gambiae where they act to modulate activation and perhaps orientation of spermatozoa, which are critical to male reproductive fitness.…”

A conditional Orco requirement in the somatic cyst cells for maintaining spermatids in a tight bundle in Drosophila testis

“…The exact function of many of these receptors outside the OSNs is still unclear. Ectopic expression and function of olfactory receptors such as MOR83, MOR8-1, MOR23, MOR127-5P and others, in the mammalian testis have been extensively studied (Vanderhaeghen et al 1993;Walensky et al 1995;Spehr et al 2004;Neuhaus et al 2006;Veitinger et al 2011;Kang and Koo 2012). Mouse olfactory receptor, OR1D2 (MOR127-5P), localizes to the mid-piece of a sperm flagellum and helps in the chemotactic navigation of the sperm towards the egg (Vanderhaeghen et al 1993;Spehr et al 2004;Neuhaus et al 2006;Veitinger et al 2011).…”