Fig. 10. Hypothetical model on the embryonic origin and dynamic gene expression profile of oligodendrocyte progenitors in embryonic spinal cord. (A) During neurogenesis stages, the ventral neuroepithelium can be divided into five domains, and each domain produces a distinct class of ventral interneuron (V0-V3) or motoneurons (MN) (adapted from Briscoe et al. (Briscoe et al., 2000). At this stage, Olig2 and Nkx2.2 are expressed in adjacent pMN domain and p3 domain, respectively. (B) Oligodendrogenesis in chicken. OLPs can be generated from both the pMN domain and p3 domain. Right before OLPs are produced from the pMN domain, expression of Nkx2.2 is dorsally expanded into the pMN domain. The OLPs that arise from the p3 domain appear to gain Olig2 expression before their terminal differentiation (see text). (C,D) Oligodendrogenesis in mouse. At the early stage of oligodendrogenesis, Nkx2.2 expression is not dorsally expanded and the Olig2+ OLPs acquire Nkx2.2 expression after migration. At later stages of oligodendrogenesis, Nkx2.2 expression is also upregulated in the pMN domain, similar to the situation in the chicken spinal cord. The p3-derived Nkx2.2+ OLPs might gain Olig2 expression after migration.
