Table 1.

Characteristics of post-mitotic neurons. (A summary of current knowledge about the different post-mitotic neuronal populations in the spinal cord. More tentative conclusions are indicated with question marks. Key references are indicated in the right-hand column. Proprioception is the kinaesthetic sense of position and movement which provides positional information about the limbs and body (i.e. the position of body parts with respect to each other). Nociception detects pain (both burning pain and sharp pain). Ipsilateral axons extend on the same side of the embryo as the cell body. Contralateral/commissural axons cross the midline and extend on the opposite side of the embryo to the cell body. Different laminae of the dorsal horn are shown in figure 2. Gene names given in the table are the official names according to the Mouse Genome Informatics web page (http://www.informatics.jax.org/). For previous and alternate gene names see table 2.)

post-mitotic interneuron population	progenitor domain origin	post-mitotic transcription factor expression	final position of cell body	axonal morphology	functional properties	key references
dI1 (called D1 in several earlier papers)	dP1 early	Lhx2, Lhx9, Barhl1, Barhl2, Pou4f1	Migrate ventrally and laterally to the deep dorsal horn.	Ascending commissural axons.	Form a subset of proprioceptor interneurons of the spino-cerebellar tracts.	Liem et al. (1997), Helms & Johnson (1998), Ben-Arie et al. (2000), Bermingham et al. (2001), Gross et al. (2002) and Saba et al. (2003)
dI1B	dP1 late	Lhx2 (not reported whether they express BarHl1 or Pou4f1)	Deep dorsal horn near, but distinct from, dI1 cells.		Probably involved in proprioception.	Lee et al. (1998)
dI2	dP2 early	Lhx1, Lhx5, Pou4f1, Foxd3	Migrate ventrally to the deep dorsal horn.	Ascending commissural interneurons.		Gowan et al. (2001) and Gross et al. (2002)
dI3 (called D2 in several earlier papers)	dP3 early	Isl1, Isl2, Pou4f1, Tlx3	Deep dorsal horn.	At least some may be ipsilateral.		Liem et al. (1997), Gross et al. (2002) and Helms et al. (2005)
dI4	dP4 early?	Lbx1h, Lhx1, Lhx5, Pax2	Laminae IV–V of dorsal horn?			Burrill et al. (1997) and Helms et al. (2005)
DILA	dP4/dP5 late?	Lbx1h, Lhx1, Lhx5, Pax2, Gbx1	Superficial laminae (I–III) of dorsal horn.		Mediate sensing of pain (nociception).	Burrill et al. (1997), Gross et al. (2002), Muller et al. (2002) and John et al. (2005)
dI5	dP5 early	Lbx1h, Pou4f1, Lmx1b, Tlx3, Tlx1, Phox2a (after migrate)	At least a subset migrate ventrally. Some cells might also migrate into the dorsal horn.			Muller et al. (2002), Qian et al. (2002) and Helms et al. (2005)
DILB	dP4/dP5 late?	Lbx1h, Pou4f1, Lmx1b, Tlx3, Prrxl1 (once in dorsal horn)	Superficial laminae (I–III) of dorsal horn.		Mediate sensing of pain (nociception).	Chen et al. (2001a,b), Gross et al. (2002), Muller et al. (2002), Qian et al. (2002) and Ding et al. (2004)
dI6	dP6 early	Lbx1h, Lhx1, Lhx5, Pax2	Migrate ventro-medially and settle in the ventral horn medial to motoneurons and close to floor plate.	At least most cells have contralateral ascending axons.		Pierani et al. (2001) and Muller et al. (2002)
V0	p0	V0V cells express Evx1+Evx2. A subset of these cells also express Pax2. V0D cells are Evx1 negative.	Migrate ventro-medially and settle in the ventral horn medial to motoneurons and close to floor plate (lamina VIII).	Contralateral ascending axons. Descend to floorplate, cross midline and extend 1–4 segments. At least most of the cells contact motoneurons.	Involved in coordinating left–right alternation in locomoter activity. 70% of V0 neurons are inhibitory and 30% are excitatory.	Briscoe et al. (2000), Moran-Rivard et al. (2001), Pierani et al. (2001) and Lanuza et al. (2004)
V1	p1 early	En1, Pax2, Foxd3	Migrate laterally and settle in the ventral horn immediately dorsal to motoneuron cell bodies in lamina VI, VII and ventral lamina IX.	Ipsilateral ascending axons. Axons project ventrally and then extend rostrally for 1–2 segments. Renshaw cells extend both rostrally and caudally.	Renshaw cells all derive from V1 cells—but they are only 10% of V1 cells. Ia and Ib inhibitory interneurons probably also derive from V1 cells. All of these interneurons fine-tune motor behaviours.	Burrill et al. (1997), Ericson et al. (1997), Saueressig et al. (1999), Briscoe et al. (2000), Pierani et al. (2001), Goulding et al. (2002) and Sapir et al. (2004)
V2	p2 early	V2a cells express Chx10+Lhx3. V2b cells express Gata2+Gata 3. Medial V2b cells also express Tal1.	Ventral horn, dorsomedial to motoneuron cell bodies but ventral to V1 interneurons.	Ipsilateral axons that project for greater than 3–5 segments caudally and rostrally?		Ericson et al. (1997), Saueressig et al. (1999), Briscoe et al. (2000), Karunaratne et al. (2002) and Smith et al. (2002)
MN	pMN	Lhx3, Isl1, Hlxb9	Ventral horn.	Axon path is determined by MN subtype identity.	Synapse directly onto muscle cells.	Jessell (2000) and Shirasaki and Pfaff (2002)
V3	p3 early	Sim1				Briscoe et al. (1999)