Decreased expression of piR-35413 in human papillary thyroid cancer

Decreased expression of piR-35413 in human papillary thyroid cancer: The piRNAs (PIWI-interacting RNAs) are ~26–31 nt in length and are very similar to but little longer than the microRNAs (miRNAs) in size [1]. Since the discovery of the first piRNA in 2006, the number of piRNA sequences has now reached 173 million from 264 datasets in 21 organisms [2]. And, there are 8,438,265 piRNAs identified in the human genome, which far exceeds the total number of miRNAs (~2000) [2], suggesting that piRNAs may play a wide variety of roles in biological activities that remain to be explored. Primarily, piRNAs have been suggested to have functions in transposon silencing by DNA methylation [3]. Following that, many functions of piRNAs were reported [1]. Of note, early reports claimed the specific expression of piRNAs in the reproduction system [4]. However, in recent studies, the expressions of piRNAs in other normal tissues or cancer tissues, such as breast cancer, gastric cancer, colorectal cancer, lung cancer, and liver cancer, have been reported [1]. But to date, there is no report demonstrating the expression of piRNA in thyroid and/or in thyroid cancer.