Abstract
The detection of external cues is fundamental for human spermatozoa to locate the oocyte in the female reproductive tract. This task requires a specific chemoreceptor repertoire that is expressed on the surface of human spermatozoa, which is not fully identified to date. Olfactory receptors (ORs) are candidate molecules and have been attributed to be involved in sperm chemotaxis and chemokinesis, indicating an important role in mammalian spermatozoa. An increasing importance has been suggested for spermatozoal RNA, which led us to investigate the expression of all 387 OR genes. This study provides the first comprehensive analysis of OR transcripts in human spermatozoa of several individuals by RNA-Seq. We detected 91 different transcripts in the spermatozoa samples that could be aligned to annotated OR genes. Using stranded mRNA-Seq, we detected a class of these putative OR transcripts in an antisense orientation, indicating a different function, rather than coding for a functional OR protein. Nevertheless, we were able to detect OR proteins in various compartments of human spermatozoa, indicating distinct functions in human sperm. A panel of various OR ligands induced Ca2+ signals in human spermatozoa, which could be inhibited by mibefradil. This study indicates that a variety of ORs are expressed at the mRNA and protein level in human spermatozoa.
Highlights
A new and unique individual can be conceived when a spermatozoon has transferred its genetic material into an oocyte
In addition to the normal mRNA-Seq data sets, we investigated stranded mRNA-Seq data sets from the human spermatozoa samples, which allowed us to investigate the orientation of the detected transcripts (Figure 1B)
We revealed the ligands for three Olfactory receptors (ORs), which were newly identified at the transcript and protein level in human sperm
Summary
A new and unique individual can be conceived when a spermatozoon has transferred its genetic material into an oocyte. Prior to fertilization of the oocyte, the spermatozoa in the female reproductive tract become hyperactivated and undergo capacitation and an acrosome reaction. On their long path to the oocyte, the spermatozoa are exposed to a number of different chemical stimuli originating from their environment, the oocyte, or its surrounding cells (Sun et al, 2005). Olfactory Receptors in Human Spermatozoa that prime sperm for fertilization. Different studies have already described receptors that are responsible for the detection of chemical molecules in mammalian spermatozoa (Spehr et al, 2003; Eisenbach and Giojalas, 2006; Martínez-López et al, 2011; Veitinger et al, 2011; Brenker et al, 2012; Meyer et al, 2012; Schiffer et al, 2014). The detection of chemical cues by human spermatozoa has not been clarified in detail
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