In platelets, splicing and translation occur in the absence of a nucleus. 
However, the integrity and stability of mRNAs derived from megakaryocyte 
progenitor cells remain poorly quantified on a transcriptome-wide level. As 
circular RNAs (circRNAs) are resistant to degradation by exonucleases, their 
abundance relative to linear RNAs can be used as a surrogate marker for mRNA 
stability in the absence of transcription. Here we show that circRNAs are 
enriched in human platelets 17- to 188-fold relative to nucleated tissues and 
14- to 26-fold relative to samples digested with RNAse R to selectively remove 
linear RNA. We compare RNAseq read depths inside and outside circRNAs to provide 
in silico evidence of transcript circularity, show that exons within circRNAs 
are enriched on average 12.7 times in platelets relative to nucleated tissues 
and identify 3162 genes significantly enriched for circRNAs, including some 
where all RNAseq reads appear to be derived from circular molecules. We also 
confirm that this is a feature of other anucleate cells through transcriptome 
sequencing of mature erythrocytes, demonstrate that circRNAs are not enriched in 
cultured megakaryocytes, and demonstrate that linear RNAs decay more rapidly 
than circRNAs in platelet preparations. Collectively, these results suggest that 
circulating platelets have lost >90% of their progenitor mRNAs and that 
translation in platelets occurs against the backdrop of a highly degraded 
transcriptome. Finally, we find that transcripts previously classified as 
products of reverse transcriptase template switching are both enriched in 
platelets and resistant to decay, countering the recent suggestion that up to 
50% of rearranged RNAs are artifacts.