Genes Dev. 2012 Nov 15;26(22):2550-9. doi: 10.1101/gad.202184.112.

Gardner EJ, Nizami ZF, Talbot CC Jr, Gall JG.

Stable intronic sequence RNA (sisRNA), a new class of noncoding RNA from the oocyte nucleus of Xenopus tropicalis.

Shows that the signal does not originate from nascent transcripts.