Mechanisms of the sperm guidance, an essential aid for meeting the oocyte

Abstract

In mammals, ejaculated spermatozoa must migrate into the female reproductive tract in order to reach and fertilize the oocyte (Figure 1). The number of spermatozoa that reach the oviductal isthmus (where they attach to oviductal cells and form the sperm reservoir) is small (1,2) and only ~10% of these spermatozoa in humans become capacitated (3) and acquire a state of readiness for fertilizing the oocyte. In addition, the sperm cells have a torturous and long way between the reservoir and the oocyte at the fertilization site (3-5 cm in humans) (2). These facts, together with the tiny dimensions of the gametes in comparison to the tube length make improbable the sperm arrival to the fertilization site and make evident the need for sperm guidance (4). Different guidance mechanisms appear essential for successful sperm arrival to the fertilization site: the short range mechanism such as chemotaxis (swimming up a chemoattractant gradient) (5) and the long range mechanisms such as rheotaxis (swimming against a fluid flow) and thermotaxis (the temperature-oriented cell motility) (Figure 1).When spermatozoa become capacitated, they acquire a number of properties that render them fertilizing ability. Thermotaxis is one of these properties in which sperm cells acquire the ability to be thermotactically active (6). This property is manifested by the ability of the capacitated spermatozoa to change their swimming direction according to a temperature gradient (towards the warmer temperature) (Figure 1). Spermatozoa can sense both the absolute ambient temperature and the temperature gradient. Previous studies showed that, at peri-ovulation stage, there is a temperature difference between the sperm reservoir site (cooler) and the fertilization site (warmer). Thus, a temperature difference of ~2 ℃ exists in rabbits between the isthmus and the isthmicampullary junction (7) and ~0.7 ℃ difference in mated pigs between the isthmus and the ampulla (8). Subsequently, Bahat and collaborators (9) demonstrated that rabbit and human spermatozoa can sense small temperature differences and respond to it by thermotaxis. These findings raised the hypothesis that the temperature difference might serve as a cue for guiding spermatozoa to the site of fertilization. Interestingly, Bahat et al.,(10) recently has reported that human spermatozoa are thermotactically responsive over a wide temperature range (29-41 ℃), much wider than the range considered physiological.As in sperm chemotaxis, only capacitated spermatozoa are thermotactically responsive (9). Additionally, in chemotaxis and thermotaxis, spermatozoa swim up the gradient by modulating the frequency of turns and hyperactivation events, essentially in the direction of the gradient (11,12).The molecular bases of sperm thermotaxis remain poorly understood. Taking into account that thermotaxis favours Editorial

Microfluidic devices employing chemo‐ and thermotaxis for sperm selection can improve sperm parameters and function in patients with high DNA fragmentation

“…A temperature difference of about 2°C exists between the storage site and fertilization site of the mammalian oviduct, leading to the hypothesis that spermatozoa can sense and swim towards the oocyte along a rising temperature gradient, known as thermotaxis (Xiao et al, 2022). Spermatozoa can sense a concentration gradient of the chemoattractant released by the cumulus oophorus complexes (CCs) as it navigates spermatozoa to the oocyte through the oviduct (Bahat & Eisenbach, 2006; Eisenbach & Giojalas, 2006; Ko et al, 2018; Lottero Leconte et al, 2017). As a result, CCs appear to be an important factor in natural sperm selection (Rappa et al, 2016).…”

The effects of red LED light on pig sperm function rely upon mitochondrial electron chain activity rather than on a PKC-mediated mechanism

“…In mammalian sperm, the TRPV4 vanilloid type of TRP receptor has been identified as the most important temperature-sensitive ion channel (Mundt et al, 2018). This is of interest, because thermotaxis has been described as a very important mechanism in the modulation of mammalian sperm function inside the female genital tract (Lottero-Leconte et al, 2017). Additionally, considering the extreme sensitivity of mammalian sperm to temperature changes as small as 0.0006 °C (Hunter, 2012), a tight control of thermotaxis-modulating systems such as TRPV4 could be important for the regulation of sperm function after ejaculation.…”

Wide-field fluorescent nanodiamond spin measurements toward real-time large-area intracellular thermometry

“…Subcellular thermometry has great potential for studying the molecular mechanisms of temperature-related biological phenomena, such as the variation of cell-death types in photothermal cancer therapy 1 – 3 , cellular thermotaxis 4 – 8 , and cellular level thermogenesis 9 – 13 . Nanodiamond (ND) spin-based thermometry is a novel opto-microwave hybrid technique that can probe subcellular temperatures with distinct photostability 14 – 18 , various functionalized surfaces 19 – 21 , and low cytotoxicity 22 – 26 .…”