Widespread proliferation and progressive fate restriction over time characterize embryonic development. During and after neural tube closure in vertebrate embryos, neural crest cells (NCC) detach from the ectoderm at the boundary between neural and non-neural epithelia, multiply and infiltrate the mesoderm. The site-appropriate differentiation of NCC is the result of a combination of extrinsic factors from the embryonic niche (1
) and cell-intrinsic properties that modify responsiveness to these influences (3
). NCC normally yields neurons and glial cells of the entire peripheral nervous system (PNS), pigment cells and endocrine cells (4
). In the head, they also give rise to cephalic tendons, cartilage, bone, dermis, meninges, vascular smooth muscle and adipocytes (5
). The original progenitors disappear along with their birthplace as the neural tube closes and matures. However, such locations as the enteric ganglia (6
), the dorsal root ganglia (7
), the hair follicle (8
), the tooth (11
) and even the bone marrow (12
) appear to be later niches for the maintenance of persistent, oligopotent avian and rodent neural crest-derived stem cells.
Because of its wide range of derivatives and long-term plasticity, the development of the neural crest has been the topic of intense study in many vertebrate species. Almost nothing is known about the endogenous characteristics of human (h)NCC, as they mix with other cell types almost immediately. Genetic errors influencing hNCC development seem to be the basis of such common birth defects as congenital heart defects, Hirschsprung disease (HSCR), labiopalatine clefting or cancers such as neuroblastoma and pheochromocytoma, collectively known as neurocristopathies (reviewed in 14
). We set out to identify molecular networks that were activated in an early hNCC population before they dispersed to their final sites of differentiation.
To address this issue, we first determined the precise time window during which hNCC separate from the developing neural tube. We then derived primary cell lines that self-renew without a feeder layer and can be propagated and frozen for many cycles. This had not been accomplished to date with NCC from any other species. Rather than focus on known pathways, we examined their entire transcriptome using SAGE to determine an intrinsic molecular profile. A subset of transcripts was validated using RT–PCR, immunohistochemistry and in situ hybridization to check representativity. When compared to published data from murine or avian counterparts, hNCC activate novel signaling pathways on top of many evolutionarily conserved modules. Furthermore, the hNCC transcriptional profile was highly evocative of the molecular signature of human embryonic stem (hES) cells, including but not restricted to the expression of the transcription factors SOX2, NANOG and POU5F1. These data indicated that after separation from the neuroepithelium, the plastic hNCC population remains poised to respond to lineage-inductive cues, using much the same transcriptional machinery as hES cells to delay differentiation.