Meeting Abstract
PIWI proteins are central players in a RNA regulatory pathway that is largely specific to the germ line and stem cells. The function of the PIWI-piRNA pathway and the identity of the pathway target genes in stem cells is, however, not well understood. Here we study the function of the Hydra PIWI homolog Hywi in stem cell maintenance within somatic stem cells. Knocking down hywi in Hydra epithelial stem cells is lethal. RNA-seq and differential gene expression analysis comparing transcript levels between 4-day old hywi RNAi juveniles and age-matched wild type siblings indicates that the PIWI-piRNA pathway represses RNA expression in these stem cells. Tissue and lineage specific RNAseq reveals that a significant fraction of the upregulated genes in RNAi animals are expressed within the differentiated cells of wild type animals. These findings lend support to the hypothesis that Hywi is required to maintain somatic stem cells by repressing differentiation genes. Furthermore, the upregulated genes include many that have been identified as injury response genes in regeneration studies. This suggests that Hywi acts upstream of a gene set that is activated during cell differentiation in wild type animals and that can be ectopically triggered by regeneration cues.
