Background: Alu repeats contribute to phylogenetic novelties in conserved regulatory networks in primates. Exaptation of Alus in transcript isoforms could nucleate large-scale mRNA-miRNA interactions and modulate cellular outcomes.
Result: Using a functional genomics approach, we report a transcript isoform of an orphan gene, CYP20A1 (CYP20A1_Alu-LT) that arise through exonization of 23 Alus in 3’UTR and is expressed in higher primates. CYP20A1_Alu-LT, confirmed by 3’RACE, is an outlier in length (9kb) and is expressed in multiple cell lines. Using publicly available datasets, we demonstrate its presence in single nucleus RNA-seq of 15928 human cortical neurons (including rosehip neurons). miRanda predicts ~4700 miRNA recognition elements (MREs; with threshold< -25kcal/mol) for ~1000 miRNAs, which have primarily originated within the 3’UTR-Alus post exonization. CYP20A1_Alu-LT could be a potential multi-miRNA sponge as it harbours ≥10 MREs for 140 miRNAs and has cytosolic localization. In order to test this further, we explored whether expression of CYP20A1_Alu-LT correlates with genome wide mRNAs harboring similar MRE targets. We carried out RNAseq with conjoint miRNA-seq analysis in primary human neurons as we observed CYP20A1_Alu-LT to be downregulated during heat shock response and upregulated in HIV1-Tat treatment. CYP20A1_Alu-LT expression was positively correlated with 380 genes that were significantly downregulated in heat shock and upregulated in Tat and harboured MREs for a set of nine expressed miRNAs that were also enriched in CYP20A1_Alu-LT. The enrichment of MREs in the 380 genes were significant compared to random sets of expressed (p=4.716e-12) as well as differentially expressed genes (p=8.134e-12). Gene ontology suggested involvement of these genes in neuronal development and hemostasis pathways.
Conclusion: Our study suggests a potential role for CYP20A1_Alu-LT as miRNA sponge due to significant enrichment of MREs within Alus in a transcript isoform specific manner. This highlights a novel component of Alu-miRNA mediated transcriptional modulation that could govern specific physiological outcomes in higher primates.