The battle of the sexes starts in the oviduct: modulation of oviductal transcriptome by X and Y-bearing spermatozoa

Abstract

Background: Sex allocation of offspring in mammals is usually considered as a matter of chance, being dependent on whether an X- or a Y-chromosome-bearing spermatozoon reaches the oocyte first. Here we investigated the alternative possibility, namely that the oviducts can recognise X- and Y- spermatozoa, and may thus be able to bias the offspring sex ratio.

Results: By introducing X- or Y-sperm populations into the two separate oviducts of single female pigs using bilateral laparoscopic insemination we found that the spermatozoa did indeed elicit sex-specific transcriptomic responses. Microarray analysis revealed that 501 were consistently altered (P-value < 0.05) in the oviduct in the presence of Y-chromosome-bearing spermatozoa compared to the presence of X-chromosome-bearing spermatozoa. From these 501 transcripts, 271 transcripts (54.1%) were down-regulated and 230 transcripts (45.9%) were up-regulated when the Y- chromosome-bearing spermatozoa was present in the oviduct. Our data showed that local immune responses specific to each sperm type were elicited within the oviduct. In addition, either type of spermatozoa elicits sex-specific signal transduction signalling by oviductal cells.

Conclusions: Our data suggest that the oviduct functions as a biological sensor that screens the spermatozoon, and then responds by modifying the oviductal environment. We hypothesize that there might exist a gender biasing mechanism controlled by the female.

Figure 1

Schematic representation of the experimental design. Sows were subjected to laparoscopic surgery. To prevent X- and Y-spermatozoa migration between oviducts, both uterine horns were cut using titanium staples. Then, one oviduct was inseminated with X-spermatozoa and the contralateral oviduct was inseminated with Y-spermatozoa (3 × 10⁵ spermatozoa/100 μl) from the same animal. Twenty-four hours following laparoscopic insemination, oviductal tissues containing X- and Y-sperm samples were collected from each side of the reproductive tract in all animals.

Figure 2

The presence of Y-spermatozoa elicited different transcriptome response within the oviduct when compared to X-spermatozoa. A: Cluster heat map analysis of the transcriptional profiles obtained from oviductal samples inseminated with X-spermatozoa and Y-spermatozoa. Each row represents a different gene, and each column displays gene expressions at different samples (X1-X4 for oviductal samples inseminated with X-spermatozoa; Y1-Y2 for oviductal samples inseminated with Y-spermatozoa). Data values displayed as yellow and blue represent elevated and reduced expression, respectively. B: A Volcano plot depicting significant changes in gene expression between oviductal samples inseminated with Y-spermatozoa and X-spermatozoa. Each of the 23,124-oligonucleotide probes is represented by a dot in the graph. The x-axis represents the fold change and the y-axis represents the statistical significance (-log10 of p-value). Transcripts showing significant differences in gene expression (501 probes, p < 0.05) are above the broken line.

Figure 3

Transcripts modulated by X-spermatozoa and Y-spermatozoa in the oviduct organized into functional categories. Transcripts differentially expressed in oviductal samples inseminated with X-spermatozoa compared to Y-spermatozoa organized into functional categories on the basis KEGG PATHWAY database.

Figure 4

Validation of the microarray results by qPCR analysis. CCL8 (chemokine (C-C motif) ligand 8) and IRF7 (interferon regulatory factor 7) expression values (normalized based on ß–actin and Ubiquitin B expression values) in oviductal samples inseminated with X-spermatozoa compared to oviductal samples inseminated with Y-spermatozoa. The expression of both transcripts in the oviductal samples inseminated with Y-spermatozoa was significantly different from that of the oviductal samples inseminated with Y-spermatozoa (P < 0.05).