Smed-myb-1 specifies early temporal identity during planarian epidermal differentiation

The planarian epidermis provides an excellent model to explore adult stem cell (ASC) lineage development due to well-characterized and distinct spatiotemporal phases during lineage progression. Using flow cytometry-isolated cells enriched in epidermal progenitors, we performed transcriptional profiling and RNAi screening to uncover regulators of epidermal differentiation. We identified a MYB-type transcription factor (Smed-myb-1) required for specification of the first temporal phase of post-mitotic maturation. Knockdown of myb-1 abolished the early progenitor phase of differentiation without ceasing production of subsequent epidermal progenitors or homeostatic turnover and regeneration of the epidermis. Further examination revealed accelerated maturation of ASC descendants, with premature entry into subsequent progeny phases and ultimately the epidermis. These results demonstrate that a spatiotemporal shift in lineage progression occurs in the absence of the early progenitor state after myb-1 RNAi, and identify myb-1 as a critical regulator of the early temporal window in the step-wise specification during planarian epidermal differentiation. control(RNAi) and Smed-myb-1(RNAi) animals were fed 3 times over 1 week. RNA was collected 6 days after the last feed. Samples were sequenced to a depth of >40 million reads. Each condition was biologically triplicated.