Abstract
Fertilization is a multiple step process leading to the fusion of female and male gametes and the formation of a zygote. Besides direct gamete membrane interaction via binding receptors localized on both oocyte and sperm surface, fertilization also involves gamete communication via chemical molecules triggering various signaling pathways. This work focuses on a mouse taste receptor, mTAS1R3, encoded by the Tas1r3 gene, as a potential receptor mediating chemical communication between gametes using the C57BL/6J lab mouse strain. In order to specify the role of mTAS1R3, we aimed to characterize its precise localization in testis and sperm using super resolution microscopy. The testis cryo-section, acrosome-intact sperm released from cauda epididymis and sperm which underwent the acrosome reaction (AR) were evaluated. The mTAS1R3 receptor was detected in late spermatids where the acrosome was being formed and in the acrosomal cap of acrosome intact sperm. AR is triggered in mice during sperm maturation in the female reproductive tract and by passing through the egg surroundings such as cumulus oophorus cells. This AR onset is independent of the extracellular matrix of the oocyte called zona pellucida. After AR, the relocation of mTAS1R3 to the equatorial segment was observed and the receptor remained exposed to the outer surroundings of the female reproductive tract, where its physiological ligand, the amino acid L-glutamate, naturally occurs. Therefore, we targeted the possible interaction in vitro between the mTAS1R3 and L-glutamate as a part of chemical communication between sperm and egg and used an anti-mTAS1R3-specific antibody to block it. We detected that the acrosome reacted spermatozoa showed a chemotactic response in the presence of L-glutamate during and after the AR, and it is likely that mTAS1R3 acted as its mediator.
Highlights
In mammals, fertilization occurs in the female reproductive tract, and after ejaculation, sperm must overcome several barriers before they reach the egg
The result of mRNA gene expression (Figure 1) suggests that the mTAS1R3 receptor, similar to CD46, is expressed in testes including male germ cells; it could be predicted to be involved in sperm-related fertilization strategies
Because we are under the impression that mTAS1R3 plays a role in short distance chemotaxis of sperm in close proximity to cumulus-oocytes complex (COC), we investigated if the exposition of acrosome-reacted sperm to anti-mouse mTAS1R3 antibody influences their chemotactic response to COC
Summary
Fertilization occurs in the female reproductive tract, and after ejaculation, sperm must overcome several barriers before they reach the egg. Only a small percentage of ejaculated sperm enters the oviduct and it is known that during their journey mammalian sperm use chemotaxis [1]. A small percentage of ejaculated sperm enters the oviduct and it is known that during their journey mammalian sperm use chemotaxis [1] This is a short-distance guidance mechanism that works only within the order of millimeters [2]. 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]. Despite all the current progress in knowledge of mouse sperm maturation, it still remains unclear whether sperm responsiveness to chemoattractants depends on sperm acrosomal status and whether sperm head could respond to the local presence of chemoattractants prior to or after the acrosome reaction
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