Abstract
The spinal cord of vertebrate animals is comprised of intrinsic circuits that are capable of sensing the environment and generating complex motor behaviors. There are two major perspectives for understanding the biology of this complicated structure. The first approaches the spinal cord from the point of view of function and is based on classic and ongoing research in electrophysiology, adult behavior, and spinal cord injury. The second view considers the spinal cord from a developmental perspective and is founded mostly on gene expression and gain-of-function and loss-of-function genetic experiments. Together these studies have uncovered functional classes of neurons and their lineage relationships. In this review, we summarize our knowledge of developmental classes, with an eye toward understanding the functional roles of each group.
Highlights
More than 20 distinct embryonic classes of neurons have been described in the spinal cord, and the developmental sources of their diversity have been elucidated over the past decade (Figure 1)
There are eight dorsal interneuron progenitor divisions, pd1–6 and the late-born pdILA and pdILB, four ventral interneuron progenitor divisions, p0–3, and one motor neuron progenitor domain, pMN (Alaynick et al, 2011). The identities of these domains are predominantly defined by basic-helix-loop-helix domain transcription factors, such as Ngn, Olig2, and Math (Bermingham et al, 2001; Gowan et al, 2001; Novitch et al, 2001; Scardigli et al, 2001; and homeodomain proteins, such as Pax3, Dbx1, and Nkx6.1 (Briscoe et al, 2000; Vallstedt et al, 2001; Subsequently, additional transcription factors, predominantly of the LIMhomeodomain family, such as Lhx1 and Isl1, are expressed in sub-groups of these domains, further refining cell fate into at least 23 distinct classes (Tsuchida et al, 1994; Gross et al, 2002; Muller et al, 2002; Thaler et al, 2002; Cheng et al, 2004)
Combinatorial transcriptional control of cell fate is a mature perspective for understanding spinal cord development
Summary
The spinal cord of vertebrate animals is comprised of intrinsic circuits that are capable of sensing the environment and generating complex motor behaviors. The first approaches the spinal cord from the point of view of function and is based on classic and ongoing research in electrophysiology, adult behavior, and spinal cord injury. The second view considers the spinal cord from a developmental perspective and is founded mostly on gene expression and gain-of-function and loss-of-function genetic experiments. Together these studies have uncovered functional classes of neurons and their lineage relationships. We summarize our knowledge of developmental classes, with an eye toward understanding the functional roles of each group.
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