Autoregulation of a Noncoding RNA Gene Figure 6. Transcription of msl2 is correlated with cell cycle. Nascent msl2 transcripts were detected with antisense FISH riboprobe in salivary glands. (A) Transgenic H83M2 expression (bright signal indicated by red triangle) was observed at the 87A insertion site in all nuclei. Hybridization to the endogenous msl2 locus at 23F (faint band indicated by red arrow in inset) was seen in only a minority of nuclei. Because of the difference in signal intensities between the two msl2 loci, the inset is enhanced to show the weaker signal. (A9) EdU incorporation shows that this is one of the few nuclei undergoing endoreplication. (B) After treatment with 1 mM of HU (hydroxyurea), no cell transcribed the endogenous msl2 gene (red arrow) but the transcription of H83M2 continued (red triangle). (B9) HU blocked EdU incorporation from any cell. (C) Simultaneous treatment of salivary glands with HU, BrUTP, and EdU showed that blocking replication did not inhibit bulk transcription in these cells. (D) Many nuclei without (left table, N = 162) or PLoS Genetics | www.plosgenetics.org 9 March 2012 | Volume 8 | Issue 3 | e1002564