Endocrine Abstracts

Background: Turner syndrome (45,X; TS) and Klinefelter syndrome (47,XXY; KS) present with a range of clinical features due to copy number aberrations of the X chromosome. The underlying genetics of these syndromes have revealed karyotype-dependent transcription and methylation patterns, and implicated genes that escape X chromosome inactivation (XCI). Alterations in the expression pattern of non-coding RNAs has previously been reported in TS and KS, yet the landscape of circular RNAs (circRNAs) has never been investigated. These endogenous circularized RNAs have the potential to facilitate regulatory processes, thereby affecting transcription, translation and epigenetics, and may contribute to the TS and KS phenotype.

Methods: Primary samples of blood, muscle and adipose tissue were collected from individuals with TS ( n= 33) and KS ( n= 22) and from males ( n= 16) and females ( n= 44) of normal karyotype. The circRNAs were identified and quantified from RNAseq data from these samples, using a combination of three different circRNA identification pipelines (CIRI2, CIRCexplorer2 and circRNA_finder). CircRNA differential expression, interaction prediction and functional enrichment analysis was carried out to describe the nature of the circRNA profile in KS and TS.

Results: Differential expression was observed throughout the genome in all tested tissues. The host-genes of these circRNAs were associated with known phenotypic traits. Furthermore, several differentially expressed circRNAs had the potential to sponge certain miRNAs and these miRNAs were predicted to interact with genes that were differentially expressed between TS and females and KS and males. CircRNAs arising specifically from the PAR-genes, displayed a general pattern of opposing expression with up-regulation in TS and down-regulation in KS, which was similar to that of their respective host-genes. Furthermore, we observed that CircRNA-miRNA-mRNA networks may compensate for altered X-chromosome dosage of the PAR-genes.

Conclusion: The present study shows pervasive changes in the circRNA transcriptome throughout three different relevant tissues in Turner and Klinefelter syndrome. It extends our understanding of TS and KS genomics, being is not only limited to changes in the mRNA transcriptome and methylome. The conceptual picture of these syndromes is clearly much more complex than hitherto thought and future studies will need to include multiple tissues, more components of the endogenous ceRNA complex, as well as the epigenome. We propose that the phenotype of these syndromes shall be seen through a lens of a complicated multi-tissue framework with multiple genomic mechanisms causing, regulating and compensating the resultant output – the patient.