Post-ejaculation thermal stress causes changes to the RNA profile of sperm in an external fertiliser

Sperm cells experience considerable post-ejaculation environmental variation. However, little is known about whether this affects their molecular composition, likely due to the assumption that sperm are transcriptionally quiescent. Nevertheless, recent evidence shows sperm have distinct RNA profiles that affect fertilisation and embryo viability. Moreover, RNAs are expected to be highly sensitive to extracellular changes. One such group of RNAs are heat shock protein (hsp) transcripts, which function in stress responses and are enriched in sperm. Here, we exploit the tractability of the mussel Mytilus galloprovincialis to exposed paired samples of ejaculated sperm to ambient (19 °C) and increased (25 °C) temperatures, then measure (a) sperm motility phenotypes, and (b) mRNA levels of two target genes (hsp70 and hsp90) and several putative reference genes. We find no phenotypic changes in motility, but reduced mRNA levels for hsp90 and the putative reference gene gapdh at 25 °C. This cou...精子细胞在射精后会面临显著的环境变异。目前学界对这类环境变化是否会影响精子的分子组成尚不清楚，这大概率源于此前普遍认为精子处于转录静止状态的认知。不过，近期研究证据表明，精子拥有独特的RNA表达谱，该表达谱可影响受精过程与胚胎存活能力。此外，RNA分子被认为对细胞外环境变化具有高度敏感性。其中一类此类RNA为热休克蛋白（heat shock protein, hsp）转录本，这类转录本参与应激反应且在精子中富集。本研究利用紫贻贝（Mytilus galloprovincialis）的易操作性，将成对的射精精子样本分别暴露于环境温度（19 ℃）与升高的温度（25 ℃）中，随后开展两项检测：(a) 精子运动表型；(b) 两个靶基因（hsp70与hsp90）以及多个候选内参基因的mRNA表达水平。研究结果显示，精子运动能力未出现显著表型变化，但在25 ℃条件下，hsp90与候选内参基因gapdh的mRNA表达水平出现下调。