Primitive neural stem cells from the mammalian epiblast differentiate to definitive neural stem cells under the control of Notch signaling

TLDR

Definitive neural stem cells that respond to FGF2 first appear at embryonic day 8.5 in mice, while earlier embryos contain neural tissue but lack these cells. The clonal sphere cells derived from early embryos display self‑renewal and neural multipotency, and although their generation is Notch‑independent, Notch activation is required for their transition to definitive neural stem cells and for maintaining that state. We identified leukemia‑inhibitory‑factor–dependent sphere‑forming cells in E5.5–E7.5 embryos, which, unlike FGF2‑dependent cells, retain some non‑neural traits, indicating they are the in‑vivo counterpart of primitive neural stem cells generated from embryonic stem cells.

Abstract

Basic fibroblast growth factor (FGF2)-responsive definitive neural stem cells first appear in embryonic day 8.5 (E8.5) mouse embryos, but not in earlier embryos, although neural tissue exists at E7.5. Here, we demonstrate that leukemia inhibitory factor-dependent (but not FGF2-dependent) sphere-forming cells are present in the earlier (E5.5–E7.5) mouse embryo. The resultant clonal sphere cells possess self-renewal capacity and neural multipotentiality, cardinal features of the neural stem cell. However, they also retain some nonneural properties, suggesting that they are the in vivo cells' equivalent of the primitive neural stem cells that form in vitro from embryonic stem cells. The generation of the in vivo primitive neural stem cell was independent of Notch signaling, but the activation of the Notch pathway was important for the transition from the primitive to full definitive neural stem cell properties and for the maintenance of the definitive neural stem cell state.