The sequencing of total RNA depleted for ribosomal sequences remains the method of choice for the study of circRNAs. Our objective was to characterize non-canonical circRNAs, namely not originating from back splicing and circRNA produced by non-coding genes. To this end, we analyzed a dataset from porcine testis known to contain about 100 intron-derived circRNAs. Labelling reads containing a circular junction and originating from back splicing provided information on the very small contribution of long non-coding genes to the production of canonical circRNAs. Analyses of the other reads revealed two origins for non-canonical circRNAs: (1) Intronic sequences for lariat-derived intronic circRNAs and intron circles, (2) Mono-exonic genes (mostly non-coding) for either a new type of circRNA (including only part of the exon: sub-exonic circRNAs) or, even more rarely, mono-exonic canonical circRNAs. The most complex set of sub-exonic circRNAs was produced by RNase_MRP (ribozyme RNA). We specifically investigated the intronic circRNA of ATXN2L, which is probably an independently transcribed sisRNA (stable intronic sequence RNA). We may be witnessing the emergence of a new non-coding gene in the porcine genome. Our results are evidence that most non-canonical circRNAs originate from non-coding sequences.

中文翻译：

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深度分析显示非编码序列产生环状RNA。

缺失核糖体序列的总RNA的测序仍然是研究circRNA的选择方法。我们的目标是鉴定非规范性circRNA，即不起源于非编码基因产生的反向剪接和circRNA。为此，我们分析了来自猪睾丸的数据集，该数据集已知包含约100个内含子衍生的circRNA。标记读物包含一个圆形连接并且源自反向剪接，提供了有关长的非编码基因对规范circRNA产生非常小的贡献的信息。对其他读物的分析揭示了非规范circRNA的两个起源：（1）套索衍生的内含circRNA和内含子圆的内含子序列，（2）两种新型circRNA（仅包括部分外显子：亚外显子circRNA），或 单外显子规范circRNA更为罕见。最复杂的亚外显子circRNA集合是由RNase_MRP（核酶RNA）。我们具体地研究的内含子circRNA ATXN2L，这可能是一个独立地转录sisRNA（稳定内含子序列的RNA）。我们可能正在目睹猪基因组中新的非编码基因的出现。我们的结果证明，大多数非规范circRNA都源自非编码序列。