Oey et al. BMC Genomics 2011, 12:315 http://www.biomedcentral.com/1471-2164/12/315 Page 8 of 10 file 1 Table S1), is similar to the relative amount of 19mers in these libraries (Figure 7). This is consistent with previously published experimental results where radioactively labelled Miwi and Mili IP RNA run on gels show no evidence of bands at 19nt [11,29]. pr19RNAs in somatic tissues We also extended our analysis to somatic tissues in order to test whether the pr19RNAs are limited to testes. For this purpose we mapped deep sequencing reads from a public small RNA dataset, which included several somatic tissues in addition to testis [14], to the IAP and LINE consensus sequences. While reads from the testis libraries produce distinct peaks at 19nt, reads from the remaining tissues produce no such peaks (Figure 8). The IAP and LINE-derived 19mers therefore seem likely to be testis specific, as concluded by Bernin- ger et al. [12] in their analysis of non-repetitive RNA. Figure 8 Distribution of LINE and IAP-derived small RNA across tissues Small RNAs from a publicly available dataset published by Chiang et al. [14]were mapped to A) an IAP consensus sequence and B) a LINE consensus sequence, and the length of the mapped reads were plotted. Only Libraries with > 100 mappable reads were included, and in the case of the LINE repeat only a representative selection of replicates from tissues and embryonic time-points are shown. The NCBI GEO [13] accession number and associated tissue annotation is shown for each dataset.