Figure 2.

Spinal cord progenitor domains give rise to distinct developmental neuron classes. Distinct progenitor domains organized along the dorsal (D) to ventral (V) axis give rise to distinct classes of neurons. Shown on the left are progenitor domains located in the ventral portion of the spinal cord, including the motor neuron progenitor (pMN) domain, four ventral progenitor domains (p0–p3), and one dorsal progenitor domain (pd6), along with the neuron classes they give rise to and molecular markers used to identify the neuron classes derived from each domain. The dorsal progenitor domains pd1–5 are not shown. The diagram of the ventral spinal cord on the right illustrates some of the properties (excitatory vs. inhibitory, ipsilateral vs. contralateral projections, etc.) as well as the interactions between ventral neuron classes. Commissural propriospinal neurons (shown on the left side of cord) project contralaterally across the midline to contact neurons on the opposite side of the spinal cord. These propriospinal neurons include dI6, V0, and V3 classes. Ipsilaterally projecting propriospinal neuron classes are shown on the right side of the cord. The broad neuronal classes may be further divided into subclasses. For example, the V1 class includes Renshaw cells (V1 RC), Ia inhibitory neurons (V1 1a), and other inhibitory neurons (V1). V2 neurons can be divided into Chx10+ V2a neurons, Gata 2/3+ V2b neurons, and Shox2 (non-Chx10+) neurons. Chx10 expressing V2a neurons can be further divided based on Shox2 expression into type I (V2a I) and type II (V2a II) neurons.