Comprehensive expression genome-wide association study of long non-coding RNAs in four porcine tissues

Background: Long non-coding RNAs (lncRNAs), a type of non-coding RNA molecules, are known to play critical regulatory roles in various biological processes. However, the functions of the majority of lncRNAs remain largely unknown, and little is understood about the regulation of lncRNA expression. In this study, high- throughput DNA genotyping and RNA sequencing were applied to investigate genomic regions associated with lncRNA expression, commonly referred to as lncRNA expression quantitative trait loci (eQTLs). We analyzed the liver, lung, spleen, and muscle transcriptomes of 100 three-way crossbred sows to identify lncRNA transcripts, explore genomic regions that might influence lncRNA expression, and identify potential regulators interacting with these regions. Result: We identified 6380 lncRNA transcripts and 3733 lncRNA genes. Correlation tests between the expression of lncRNAs and protein-coding genes were performed. Subsequently, functional enrichment analyses were carried out on protein-coding genes highly correlated with lncRNAs. Our correlation results of these protein-coding genes uncovered terms that are related to tissue specific functions. Additionally, heatmaps of lncRNAs and protein-coding genes at different correlation levels revealed several distinct clusters. An expression genome-wide association study (eGWAS) was conducted using 535,896 genotypes and 1829, 1944, 2089, and 2074 expressed lncRNA genes for liver, spleen, lung, and muscle, respectively. This analysis identified 520,562 significant associations and 6654, 4525, 4842, and 7125 eQTLs for the respective tissues. Only a small portion of these eQTLs were classified as cis-eQTLs. Fifteen regions with the highest eQTL density were selected as eGWAS hotspots and potential mechanisms of lncRNA regulation in these hotspots were explored. However, we did not identify any interactions between the transcription factors or miRNAs in the hotspots and the lncRNAs, nor did we observe a significant enrichment of regulatory elements in these hotspots. While we could not pinpoint the key factors regulating lncRNA expression, our results suggest that the regulation of lncRNAs involves more complex mechanisms. Conclusion: Our findings provide insights into several features and potential functions of lncRNAs in various tissues. However, the mechanisms by which lncRNA eQTLs regulate lncRNA expression remain unclear. Further research is needed to explore the regulation of lncRNA expression and the mechanisms underlying lncRNA interactions with small molecules and regulatory proteins.