Figure 1.

There is substantial variation in the number of circRNAs across databases. Number of unique circRNAs in the (A) noncurated and (B) curated databases. Most databases solely contain human circRNAs, but some also include circRNAs detected in other species. The number of circRNAs differs greatly between and within noncurated and curated databases. The differences within noncurated circRNA databases can mostly be explained by different starting material, sequencing method, circRNA detection tools and filtering steps. The differences within curated databases can partly be explained by different selection criteria of empirically validated circRNAs, despite similar search strategies.