RPL15 and cyst: Interestingly, the signal intensities of 5.8S, 18S, 28S rRNAs, and Rpl15 were low in a portion of wild-type 1- to 2-cell cyst spermatogonia (Figure 2A), suggesting the presence of two populations also in the rRNA concentrations (low and high) in the 1- to 2-cell stage.