Taste Receptors: New Players in Sperm Biology

Abstract

Taste receptors were first described as sensory receptors located on the tongue, where they are expressed in small clusters of specialized epithelial cells. However, more studies were published in recent years pointing to an expression of these proteins not only in the oral cavity but throughout the body and thus to a physiological role beyond the tongue. The recent observation that taste receptors and components of the coupled taste transduction cascade are also expressed during the different phases of spermatogenesis as well as in mature spermatozoa from mouse to humans and the overlap between the ligand spectrum of taste receptors with compounds in the male and female reproductive organs makes it reasonable to assume that sperm “taste” these different cues in their natural microenvironments. This assumption is assisted by the recent observations of a reproductive phenotype of different mouse lines carrying a targeted deletion of a taste receptor gene as well as the finding of a significant correlation between human male infertility and some polymorphisms in taste receptors genes. In this review, we depict recent findings on the role of taste receptors in male fertility, especially focusing on their possible involvement in mechanisms underlying spermatogenesis and post testicular sperm maturation. We also highlight the impact of genetic deletions of taste receptors, as well as their polymorphisms on male reproduction.

The Role of Taste Receptor mTAS1R3 in Chemical Communication of Gametes

“…Interestingly, it was discovered that the mRNA expression level was highest in the testis (Figure 1). This result indicated the importance of mTAS1R3 in reproduction and mainly in male fertility, which is supported by the evidence that TAS1 receptors are involved in spermiogenesis or the post-testicular maturation of sperm [5,10].…”

“…Positive chemotaxis is a directed movement up a concentration gradient of chemical factors, called chemoattractants, which influence receptors on the sperm surface and modulate sperm behavior [2][3][4]. Key physiological sperm maturation processes such as the capacitation, hyperactivation and acrosome reaction are triggered during the passage of sperm through the female reproductive tract and they are potentially sensitive to chemotactic mechanisms [5].…”

“…Taste receptors are not only present in the oral cavity; they also occur in many other tissues [5]. Importantly, the presence of all three members of the TAS1R subfamily, mTAS1R1, mTAS1R2 and mTAS1R3, were observed in mouse testis and knockout mice proved the importance of these receptors for physiological sperm development [21].…”

Longitudinal Expression of Testicular TAS1R3 from Prepuberty to Sexual Maturity in Congjiang Xiang Pigs

“…Interestingly, many initial components of sweet/umami taste signaling cascades, such as PLCβ2, G protein γ13 subunit (Gγ13), and transient receptor potential channel M5 (TRPM5), are also expressed in testicular Leydig cells and late spermatogenic cells [7,8]. In addition, T1R1/T1R3 expressed in the flagella and acrosomal cap of sperm in mice regulates basal Ca 2+ and cAMP levels during sperm development, maturation, and fertilization [6,9]. Genetic absence of both Tas1r3 and G protein subunit alpha transducin 3 (Gnat3) leads to specific sterility in male mice [10].…”

“…Owing to the role of T1R3/Gαgust in spermatogenesis and steroidogenesis in the mouse testis [9,11,12], we hypothesized that TAS1R3 contributes to testis development in the Congjiang Xiang pig, a rare Chinese indigenous breed characterized by a small body size, with an adult body weight of approximately 40 kg (while other minipigs are about 60 kg) [13]. They reach sexual maturity at the age of around 3−4 months and have high disease resistance, favorable meat quality and strong adaptability [13][14][15].…”