Abstract
Simple SummaryTaste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, is widely expressed from the tongue to the testis, and testis expression is associated with male sterility. In Congjiang Xiang pigs, T1R3 is expressed in elongating/elongated spermatids and Leydig cells in a stage-dependent manner during postnatal development and the spermatogenic cycle. T1R3 may contribute to regulation of spermatid differentiation and Leydig cell function, and may therefore help limit the incidence of various male reproductive pathologies.Testicular expression of taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, has been implicated in spermatogenesis and steroidogenesis in mice. We explored the role of testicular T1R3 in porcine postnatal development using the Congjiang Xiang pig, a rare Chinese miniature pig breed. Based on testicular weights, morphology, and testosterone levels, four key developmental stages were identified in the pig at postnatal days 15–180 (prepuberty: 30 day; early puberty: 60 day; late puberty: 90 day; sexual maturity: 120 day). During development, testicular T1R3 exhibited stage-dependent and cell-specific expression patterns. In particular, T1R3 levels increased significantly from prepuberty to puberty (p < 0.05), and expression remained high until sexual maturity (p < 0.05), similar to results for phospholipase Cβ2 (PLCβ2). The strong expressions of T1R3/PLCβ2 were observed at the cytoplasm of elongating/elongated spermatids and Leydig cells. In the eight-stage cycle of the seminiferous epithelium in pigs, T1R3/PLCβ2 levels were higher in the spermatogenic epithelium at stages II–VI than at the other stages, and the strong expressions were detected in elongating/elongated spermatids and residual bodies. The message RNA (mRNA) levels of taste receptor type 1 subunit 1 (T1R1) in the testis showed a similar trend to levels of T1R3. These data indicate a possible role of T1R3 in the regulation of spermatid differentiation and Leydig cell function.
Highlights
Taste sensations enable animals to evaluate which prospective foods are nutritious or toxic
The accelerated increase in the testis weight and testis index at postnatal 60 day corresponded with higher levels of plasma testosterone than those at 15 day (p = 0.0007) and 30 day (p < 0.0001); plasma testosterone mainly acts via androgen receptors on Sertoli cells to maintain normal testicular function (Figure 2)
An IHC analysis showed that the strong expressions of testicular T1R3/phospholipase Cβ2 (PLCβ2) were detected at the cytoplasm of elongating/elongated spermatids and Leydig cells
Summary
Taste sensations enable animals to evaluate which prospective foods are nutritious or toxic. Members of the taste receptor family 1 (T1Rs), encoded by TAS1R genes, T1Rs are largely responsible for sensing sweet and umami tastes in the taste buds. Taste receptor family 1 subunit 1 (T1R1)/taste receptor family 1 subunit 3 (T1R3) heterodimers form an umami taste receptor, and the taste receptor family 1 subunit 2 (T1R2)/T1R3 heterodimers recognize sweet tastes [1]. A heterotrimeric GTP-binding protein (gustducin)mediated signaling cascade can be activated when T1Rs sense umami or sweet stimuli. A. GTP-protein consisting of 2 subunits, α-gustducin (Gαgust) and βγ-gustducin (Gβγgust), activates phospholipase Cβ2 (PLCβ2) to increase intracellular Ca2+ levels. Gαgust is expected to activate phosphodiesterase (PDE), resulting in decreased intracellular cyclic adenosine monophosphate (cAMP) levels after ligand binding [1]
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