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.
Highlights
The elongated duct presenting the epididymis at the, where the luminal fluid of each region is characterized by a unique composition of posterior margin of the testis is subdivided into three discrete segments, where different constituents, essential for post-testicular sperm maturation
Due to the similarity of the histological phenotype of Tas1r3/gustducin and cAMP responsive element modulator (CREM) null males as well as the observation that CREM is highly expressed in postmeiotic cells of the testis [144,145] one might suggest that CREM, via a taste receptor controlled cAMP pathway, is responsible in ensuring exactness of germ cell development
By in silico analyses, we demonstrated a functional effect of the two SNPs: TAS2R14-rs3741843 in regulating TAS2R43 expression. Since this latter is known to be expressed in the human airway epithelia where it is involved in the regulation of ciliary movements to eliminate toxic substances [32], we suggested that it could participate in sperm motility
Summary
The name “Taste receptors” (TAS) derives from their first identification in the oral cavity [1]. The taste 2 receptors, consisting of a large family including about 25 different isoforms in humans and about 35 in rodents, are responsible for the sensation of bitter tastants [12,17,18] The signalling of both TAS1Rs and TAS2Rs is mediated by the same intracellular transduction pathway in type II taste bud cells [10,19,20] (Figure 1). The binding of the corresponding ligand activates a heterotrimeric G protein, which consists in most cells of the G protein α-gustducin and β3 /γ13 , leading to the release of the G β/γ subunits and a subsequent stimulation of phospholipase C isoform β2 (PLCβ2), which, in turn, hydrolyses the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2 ) to produce the two second messengers inositol 1,4,5-triphosphate (IP3 ) and diacylglycerol (DAG) [8,10,20]. Released α-gustducin activates phosphodiesterase, resulting in a decrease of intracellular levels of the second messenger cyclic adenosine monophosphate (cAMP) [28]
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