Krüppel-like Factors Play Essential Roles in Regulating Pluripotency and the Formation of Neural Crest Stem Cells.

The evolutionary transition from simple chordate body plans to complex vertebrate body plans was driven by the acquisition of the neural crest, a stem cell population that retains broad, multi-germ layer developmental potential long after most embryonic cells have become lineage restricted. We have previously shown that neural crest cells share significant gene regulatory architecture with pluripotent blastula stem cells. Here we examine the roles that Krüppel-like Family (Klf) transcription factors play in these stem cell populations. Although Klf4 has established roles in regulating pluripotency in mammalian stem cells cultures, we find that in it is that is highly expressed in pluripotent blastula stem cells. expression is down-regulated as cells transition to a neural crest state while a related klf factor, klf17, is significantly up regulated in response to neural crest induction. We used gain and loss of function studies to compare the activities of these closely related factors and found that they have both shared and distinct activities. Inhibition of either klf2 or klf17 activity led to significantly expanded expression of pluripotency, neural plate border and neural crest factors in neurula stage embryos, leading us to hypothesize that klf factors regulate the exit from pluripotency and proper establishment of the boundary of the neural crest domain. To gain further insights into the role of klf factors in the evolution of the neural crest, we examined their expression in the jawless vertebrate, sea lamprey). We find that lamprey have a and a gene, but that only is expressed in blastula and neural crest stem cells. Moreover, ectopic expression of lamprey in embryos phenocopies activity. These data suggest that klf17, rather than klf4, may have been the ancestral klf factor that functioned in these GRNs in stem vertebrates.