Activation of Toll-like receptor 7/8 encoded by the X chromosome alters sperm motility and provides a novel simple technology for sexing sperm

Abstract

In most mammals, the male to female sex ratio of offspring is about 50% because half of the sperm contain either the Y chromosome or X chromosome. In mice, the Y chromosome encodes fewer than 700 genes, whereas the X chromosome encodes over 3,000 genes. Although overall gene expression is lower in sperm than in somatic cells, transcription is activated selectively in round spermatids. By regulating the expression of specific genes, we hypothesized that the X chromosome might exert functional differences in sperm that are usually masked during fertilization. In this study, we found that Toll-like receptors 7/8 (TLR7/ 8) coding the X chromosome were expressed by approximately 50% of the round spermatids in testis and in approximately 50% of the epididymal sperm. Especially, TLR7 was localized to the tail, and TLR8 was localized to the midpiece. Ligand activation of TLR7/8 selectively suppressed the mobility of the X chromosome-bearing sperm (X-sperm) but not the Y-sperm without altering sperm viability or acrosome formation. The difference in sperm motility allowed for the separation of Y-sperm from X-sperm. Following in vitro fertilization using the ligand-selected high-mobility sperm, 90% of the embryos were XY male. Likewise, 83% of the pups obtained following embryo transfer were XY males. Conversely, the TLR7/8-activated, slow mobility sperm produced embryos and pups that were 81% XX females. Therefore, the functional differences between Y-sperm and X-sperm motility were revealed and related to different gene expression patterns, specifically TLR7/8 on X-sperm. Activation of Toll-like receptor 7/8 encoded by the X chromosome alters sperm motility and provides a novel simple technology for sexing sperm. PLoS Biol 17(8): e3000398. https://doi.including the nuclear condensation, acrosome formation, and the elongation of the sperm flagella [3,4]. As indicated by studies using knockout mouse models, the morphological changes associated with spermiogenesis are associated with the expression of various genes, including Tekt, Tnp, and Gba2 in the round spermatids [5][6][7]. Thus, active gene transcription occurs on chromosomes, including sex chromosomes, in haploid male germ cells, and some of them are essential for cell survival [8]. Using the cytoplasmic bridges between spermatids, cytoplasm including RNAs and proteins are shared to rescue Y chromosome bearing sperm (Y-sperm) [8,9]. It has been reported that the bridge works in spermatid at early stage of spermiogenesis, and the high levels of RNA polymerase II are detected in this stage [10,11]. However, RNA polymerase II is still detected in later stages of spermiogenesis [11], indicating that the unique features of sperm can be distinguished not only by the presence of the X or Y chromosome but also by expression of distinct genes encoded by each sex chromosome.However, mouse Y chromosome encodes fewer than 700 genes, whereas mouse X chromosome encodes over 3,000 genes [12,13]. The X chromosome contains some unique genes, such as Taz encoding tafazzin that is a t...

Targeting of the Dosage-Compensated Male X-Chromosome during Early Drosophila Development

“…If dosage compensation was significantly affected by the autosomal SD system, then a strong male-specific viability defect would be expected, but the autosomal SD system does not cause a strong sex bias (Denell et al, 1969). Recently, meiotic drive has also been used to sex select mouse embryos, but this system has not yet been used to study dosage compensation (Umehara et al, 2019).…”

Sex and suicide: The curious case of Toll-like receptors

“…Umehara and colleagues recently reported that the membrane-associated receptor proteins Toll-like receptor (TLR) 7 and TLR8 can be used to separate mouse sperm cell fractions enriched either for X or Y chromosome-bearing sperm [1]. According to this study, Xencoded TLR7/8 are predominantly expressed in X-bearing sperm, and the activation of these receptors reduces sperm cell motility.…”

“…A gene that impedes its own reproductive success should be rapidly selected against and unable to persist in the population [2]. Below, we address various aspects of this mystery, focusing specifically on two key questions: (1) How are TLR7/8 specifically enriched in X-bearing sperm cells? And (2) what are the possible evolutionary consequences of this peculiar haploid selection mechanism?…”

Widespread haploid-biased gene expression in mammalian spermatogenesis associated with frequent selective sweeps and evolutionary conflict

“…In light of this finding, a number of cases of sperm-level functional differences in the literature can be putatively attributed to GIMs (Conway et al 1994; P. A. Martin-DeLeon et al 2005; Butler et al 2007; Véron et al 2009; Cocquet et al 2012; Alavioon et al 2017; Nadeau 2017; Umehara, Tsujita, and Shimada 2019). Despite the growing number of examples of sperm-mediated transmission ratio distortion, it has been widely assumed these are isolated cases and that mammalian sperm are functionally diploid as a rule.…”

“…In a mouse model for Niemann-Pick disease, heterozygous knockouts of Smpd1 have sperm with functional differences in mitochondrial membrane potential associated with their genotype (Butler et al 2007). Recently, TLR7/8 inhibitors have been reported to differentially affect sperm with the X or Y chromosome (Umehara, Tsujita, and Shimada 2019). Nevertheless, it is widely assumed that most gene products are shared between mammalian gametes, erasing any allelic expression bias.…”