Shared and individual expression patterns of pluripotency genes in the developing chick embryo during neurulation and beyond.

The neural crest (NC) is a transient population of pluripotent-like, pleistopotent stem cells that emerges early in vertebrate development. These cells play a pivotal role in generating a diverse array of tissues, including the craniofacial bone and cartilage, the entire peripheral nervous system, melanocytes of the skin, certain cardiac structures, and chromaffin cells of the adrenal medulla, among others. The stem cell potential of neural crest cells (NCCs) has long intrigued developmental biologists, as the NC originates post-gastrulation in the ectoderm, yet NCCs also give rise to derivatives typically associated with mesodermal or endodermal origins. Recent work has shown that NCCs co-express factors known from the core pluripotency complex from the pre-gastrulation stages in the epiblast, which enables their exceptionally high stem cell potential. However, detailed spatiotemporal data on pluripotency factor expression in vertebrate embryos remain limited, and the distinction between the function of co-expression of pluripotency genes versus their individual expression in the developing embryo is not clear. In this study, to elucidate the NCC formation process across axial levels as well as the putative different roles of these stem cell genes during early embryogenesis, we used multi-channel fluorescent in situ hybridization to comprehensively examine the anterior-to-posterior expression of pluripotency factors PouV (Oct4), Nanog, Klf4 and Lin28A in chick embryos across key developmental stages, from Hamburger and Hamilton (HH) stage 5 to stage 14. From head to trunk, we find that while the early ectoderm, including the future epidermis and central nervous system (CNS) domains, in the neural fold stages broadly co-express these genes, their expression profiles differ significantly after neurulation. Nanog expression remains in the hindbrain and vagal migratory NCCs. Klf4 strongly marks the developing floor plate, and Klf4, PouV and Lin28A are expressed also in the neural tube that forms the CNS as well as in the developing somites, implying additional roles for these factors during embryogenesis.