Abstract
BackgroundAlthough sperm is transcriptionally and translationally quiescent, complex populations of RNAs, including mRNAs and non-coding RNAs, exist in sperm. Previous microarray analysis of germ cell mutants identified hundreds of sperm genes in Caenorhabditis elegans. To take a more comprehensive view on C. elegans sperm genes, here, we isolate highly pure sperm cells and employ high-throughput technologies to obtain sperm transcriptome and proteome.ResultsFirst, sperm transcriptome consists of considerable amounts of non-coding RNAs, many of which have not been annotated and may play functional roles during spermatogenesis. Second, apart from kinases/phosphatases as previously reported, ion binding proteins are also enriched in sperm, underlying the crucial roles of intracellular ions in post-translational regulation in sperm. Third, while the majority of sperm genes/proteins have low abundance, a small number of sperm genes/proteins are hugely enriched in sperm, implying that sperm only rely on a small set of proteins for post-translational regulation. Lastly, by extensive RNAi screening of sperm enriched genes, we identified a few genes that control fertility. Our further analysis reveals a tight correlation between sperm transcriptome and sperm small RNAome, suggesting that the endogenous siRNAs strongly repress sperm genes. This leads to an idea that the inefficient RNAi screening of sperm genes, a phenomenon currently with unknown causes, might result from the competition between the endogenous RNAi pathway and the exogenous RNAi pathway.ConclusionsTogether, the obtained sperm transcriptome and proteome serve as valuable resources to systematically study spermatogenesis in C. elegans.
Highlights
Sperm is transcriptionally and translationally quiescent, complex populations of RNAs, including mRNAs and non-coding RNAs, exist in sperm
Sequencing C. elegans sperm transcriptome and proteome We performed large-scale culturing of C. elegans strain him-5, followed by isolating males and purifying sperm, and obtained highly pure sperm cells
Trace H3K4 methylation mark has been detected in mammalian sperm [1,5,7]; here, we show C. elegans sperm retain histone methylation mark (Figure 1b)
Summary
Sperm is transcriptionally and translationally quiescent, complex populations of RNAs, including mRNAs and non-coding RNAs, exist in sperm. Reinke et al identified sets of genes that are spermatogenesis-enriched, oogenesisenriched and sex-regulated [28,29] Their analyses showed that the sperm-enriched genes encode considerable numbers of kinases and phosphatases, and are depleted from the X-chromosome, echoing the findings of Reuben et al that the X-chromosome in males exhibits striking H3K9 methylation [30]. These microarray analyses identified sperm genes on a large-scale; the analyses were based on comparisons between germ cell mutants, and purified sperm cells were not used. Their microarray analyses only identified sperm-enriched genes, while omitted those sperm genes that are abundant in oocyte
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