RNA Seq analysis in flatworm following 6, 12, or 18 day treatment with RNAi against Pax5, Sox8, or Zfp1, relative to unc22 to identify transcriptional targets.. Schmidtea mediterranea

Epidermis is essential for animal survival, providing both a protective barrier and cellular sensor to the external environment. Interestingly, the epidermes of different species show broad morphological and functional diversity yet it is unclear whether this diversity came from modification of an existing gene regulatory network or de novo innovation of new genes. Here we identify the transcriptional regulators underlying the differentiation program of planarian epidermal lineage. We classify Smed-p53 as the most upstream molecule in this transcriptional cascade, suggesting a potentially conserved role for this gene in epidermal differentiation similar to TP63 in vertebrates. Moreover, we find that homologs of Sox and Pax family transcription factors, Smed-soxP-3 and Smed-pax-5, act cooperatively to activate the expression of epidermal markers. Together, these data show that planarian epidermal differentiation is regulated by a combination of conserved elements (p53/p63), recruitment of a non-conventional transcription module (soxP-3/pax-5), and novel genes (prog); they also suggest that specialized adpatations, such as epidermal mucus-secretion, arise from complex changes to gene networks. Overall design: Examine gene expression profiles of adult flatworms after 6, 12, or 18 days of treatment with RNAi against either Pax5, Sox8, Zfp, or an unc22 non-targeting control. The experiment was performed in quadruplicate resulting in 48 samples.