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Expression of Tas1 taste receptors in mammalian spermatozoa: functional role of Tas1r1 in regulating basal Ca²⁺ and cAMP concentrations in spermatozoa.

Meyer D, Voigt A, Widmayer P, Borth H, Huebner S, Breit A, Marschall S, de Angelis MH, Boehm U, Meyerhof W, Gudermann T, Boekhoff I - PLoS ONE (2012)

Bottom Line: The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head.Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities.Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes.

View Article: PubMed Central - PubMed

Affiliation: Walther-Straub Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University, Munich, Germany.

ABSTRACT

Background: During their transit through the female genital tract, sperm have to recognize and discriminate numerous chemical compounds. However, our current knowledge of the molecular identity of appropriate chemosensory receptor proteins in sperm is still rudimentary. Considering that members of the Tas1r family of taste receptors are able to discriminate between a broad diversity of hydrophilic chemosensory substances, the expression of taste receptors in mammalian spermatozoa was examined.

Methodology/principal findings: The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head. Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities. In addition, a significant increase in spontaneous acrosomal reaction was observed in Tas1r1 mutant sperm whereas acrosomal secretion triggered by isolated zona pellucida or the Ca²⁺ ionophore A23187 was not different from wild-type spermatozoa. Remarkably, cytosolic Ca²⁺ levels in freshly isolated Tas1r1-deficient sperm were significantly higher compared to wild-type cells. Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes.

Conclusions/significance: Since Ca²⁺ and cAMP control fundamental processes during the sequential process of fertilization, we propose that the identified taste receptors and coupled signaling cascades keep sperm in a chronically quiescent state until they arrive in the vicinity of the egg - either by constitutive receptor activity and/or by tonic receptor activation by gradients of diverse chemical compounds in different compartments of the female reproductive tract.

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Sperm count and testosterone level of Tas1r1/mCherry knock-inmice.[A] Total number of caudal epididymal sperm inTas1r1 -mutant mice. Number of sperm in the caudal part of theepididymis were counted in male wild-type[+/+], heterozygous[+/−] and homozygous[−/−] mutantTas1r1 animalswith identical strain background. Data are mean values ±SEM of17–46 animals of the three genotypes. [B]Serum testosterone levels in Tas1r1-deficient male mice. Testosteroneconcentrations were measured in 4–6 month old male littermates ofwild-type [+/+], heterozygous[+/−] and homozygous[−/−] Tas1r1 mice by acommercial enzyme-linked immunoassay. Data, expressed as means ±SEM, are obtained from 3 animals of each genotype with triplicatedeterminations; statistical analysis was done by a pairedT-test; a p-value of ≤0.05 was considered to bestatistically significant.
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pone-0032354-g007: Sperm count and testosterone level of Tas1r1/mCherry knock-inmice.[A] Total number of caudal epididymal sperm inTas1r1 -mutant mice. Number of sperm in the caudal part of theepididymis were counted in male wild-type[+/+], heterozygous[+/−] and homozygous[−/−] mutantTas1r1 animalswith identical strain background. Data are mean values ±SEM of17–46 animals of the three genotypes. [B]Serum testosterone levels in Tas1r1-deficient male mice. Testosteroneconcentrations were measured in 4–6 month old male littermates ofwild-type [+/+], heterozygous[+/−] and homozygous[−/−] Tas1r1 mice by acommercial enzyme-linked immunoassay. Data, expressed as means ±SEM, are obtained from 3 animals of each genotype with triplicatedeterminations; statistical analysis was done by a pairedT-test; a p-value of ≤0.05 was considered to bestatistically significant.

Mentions: The observed increase in programmed cell death in Tas1r1-deficient mice did notlead to decreased testis weight (Table 3); however, disturbances in spermiogenesis (Fig. 5 and 6) could result in a reducednumber of mature sperm cells and/or in non-functional spermatozoa. Therefore, wecounted the number of mature spermatozoa isolated from the caudal part of theepididymis of Tas1r1/mCherry homozygous, heterozygous and wild-type male animals(Fig. 7A). In addition,the concentration of testosterone, essential for qualitatively andquantitatively normal spermatogenesis [63], [64], was analyzed in serum ofthe three genotypes (Fig.7B). The total number of sperm obtained from the cauda epididymidis ofall three genotypes was comparable (Fig. 7A); likewise, there was no difference in testosterone levelsbetween wild-type and the two Tas1r1 genotypes (Fig. 7B). Moreover, examining germ cellmorphology, we found that Tas1r1-deficient sperm do not exhibit obviousstructural defects compared to wild-type sperm (Fig. 8A): Tas1r1 sperm possess anormally formed flagellum and exhibit the characteristic hook-shaped outline ofthe head typical for mouse sperm. A quantitative morphometric analysis of thehead (for parameters see Fig.8B) confirmed this impression: Data summarized in figure 8C document thatcircumference and area of the sperm head were not different between the twogenotypes ([III, IV]); similarresults were obtained when measuring the length of the sperm head (Fig. 8C,[I]) and the distance between the proximal anddistal ends of the acrosome (Fig.8C; [II]).


Expression of Tas1 taste receptors in mammalian spermatozoa: functional role of Tas1r1 in regulating basal Ca²⁺ and cAMP concentrations in spermatozoa.

Meyer D, Voigt A, Widmayer P, Borth H, Huebner S, Breit A, Marschall S, de Angelis MH, Boehm U, Meyerhof W, Gudermann T, Boekhoff I - PLoS ONE (2012)

Sperm count and testosterone level of Tas1r1/mCherry knock-inmice.[A] Total number of caudal epididymal sperm inTas1r1 -mutant mice. Number of sperm in the caudal part of theepididymis were counted in male wild-type[+/+], heterozygous[+/−] and homozygous[−/−] mutantTas1r1 animalswith identical strain background. Data are mean values ±SEM of17–46 animals of the three genotypes. [B]Serum testosterone levels in Tas1r1-deficient male mice. Testosteroneconcentrations were measured in 4–6 month old male littermates ofwild-type [+/+], heterozygous[+/−] and homozygous[−/−] Tas1r1 mice by acommercial enzyme-linked immunoassay. Data, expressed as means ±SEM, are obtained from 3 animals of each genotype with triplicatedeterminations; statistical analysis was done by a pairedT-test; a p-value of ≤0.05 was considered to bestatistically significant.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3303551&req=5

pone-0032354-g007: Sperm count and testosterone level of Tas1r1/mCherry knock-inmice.[A] Total number of caudal epididymal sperm inTas1r1 -mutant mice. Number of sperm in the caudal part of theepididymis were counted in male wild-type[+/+], heterozygous[+/−] and homozygous[−/−] mutantTas1r1 animalswith identical strain background. Data are mean values ±SEM of17–46 animals of the three genotypes. [B]Serum testosterone levels in Tas1r1-deficient male mice. Testosteroneconcentrations were measured in 4–6 month old male littermates ofwild-type [+/+], heterozygous[+/−] and homozygous[−/−] Tas1r1 mice by acommercial enzyme-linked immunoassay. Data, expressed as means ±SEM, are obtained from 3 animals of each genotype with triplicatedeterminations; statistical analysis was done by a pairedT-test; a p-value of ≤0.05 was considered to bestatistically significant.
Mentions: The observed increase in programmed cell death in Tas1r1-deficient mice did notlead to decreased testis weight (Table 3); however, disturbances in spermiogenesis (Fig. 5 and 6) could result in a reducednumber of mature sperm cells and/or in non-functional spermatozoa. Therefore, wecounted the number of mature spermatozoa isolated from the caudal part of theepididymis of Tas1r1/mCherry homozygous, heterozygous and wild-type male animals(Fig. 7A). In addition,the concentration of testosterone, essential for qualitatively andquantitatively normal spermatogenesis [63], [64], was analyzed in serum ofthe three genotypes (Fig.7B). The total number of sperm obtained from the cauda epididymidis ofall three genotypes was comparable (Fig. 7A); likewise, there was no difference in testosterone levelsbetween wild-type and the two Tas1r1 genotypes (Fig. 7B). Moreover, examining germ cellmorphology, we found that Tas1r1-deficient sperm do not exhibit obviousstructural defects compared to wild-type sperm (Fig. 8A): Tas1r1 sperm possess anormally formed flagellum and exhibit the characteristic hook-shaped outline ofthe head typical for mouse sperm. A quantitative morphometric analysis of thehead (for parameters see Fig.8B) confirmed this impression: Data summarized in figure 8C document thatcircumference and area of the sperm head were not different between the twogenotypes ([III, IV]); similarresults were obtained when measuring the length of the sperm head (Fig. 8C,[I]) and the distance between the proximal anddistal ends of the acrosome (Fig.8C; [II]).

Bottom Line: The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head.Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities.Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes.

View Article: PubMed Central - PubMed

Affiliation: Walther-Straub Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University, Munich, Germany.

ABSTRACT

Background: During their transit through the female genital tract, sperm have to recognize and discriminate numerous chemical compounds. However, our current knowledge of the molecular identity of appropriate chemosensory receptor proteins in sperm is still rudimentary. Considering that members of the Tas1r family of taste receptors are able to discriminate between a broad diversity of hydrophilic chemosensory substances, the expression of taste receptors in mammalian spermatozoa was examined.

Methodology/principal findings: The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head. Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities. In addition, a significant increase in spontaneous acrosomal reaction was observed in Tas1r1 mutant sperm whereas acrosomal secretion triggered by isolated zona pellucida or the Ca²⁺ ionophore A23187 was not different from wild-type spermatozoa. Remarkably, cytosolic Ca²⁺ levels in freshly isolated Tas1r1-deficient sperm were significantly higher compared to wild-type cells. Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes.

Conclusions/significance: Since Ca²⁺ and cAMP control fundamental processes during the sequential process of fertilization, we propose that the identified taste receptors and coupled signaling cascades keep sperm in a chronically quiescent state until they arrive in the vicinity of the egg - either by constitutive receptor activity and/or by tonic receptor activation by gradients of diverse chemical compounds in different compartments of the female reproductive tract.

Show MeSH
Related in: MedlinePlus