Abstract
IntroductionDuring vertebrate development, the central nervous system (CNS) has stereotyped neuronal tracts (scaffolds) that include longitudinal and commissural axonal bundles, such as the medial longitudinal fascicle or the posterior commissure (PC). As these early tracts appear to guide later-developing neurons, they are thought to provide the basic framework of vertebrate neuronal circuitry. The proper construction of these neuronal circuits is thought to be a crucial step for eliciting coordinated behaviors, as these circuits transmit sensory information to the integrative center, which produces motor commands for the effective apparatus. However, the developmental plan underlying some commissures and the evolutionary transitions they have undergone remain to be elucidated. Little is known about the role of axon guidance molecules in the elicitation of early-hatched larval behavior as well.ResultsHere, we report the developmentally regulated expression pattern of axon-guidance molecules Slit2 ligand and Robo2 receptor in Xenopus laevis and show that treatment of X. laevis larvae with a slit2- or robo2-morpholino resulted in abnormal swimming behavior. We also observed an abnormal morphology of the PC, which is part of the early axonal scaffold.ConclusionOur present findings suggest that expression patterns of Slit2 and Robo2 are conserved in tetrapods, and that their signaling contributes to the construction of the PC in Xenopus. Given that the PC also includes several types of neurons stemming from various parts of the CNS, it may represent a candidate prerequisite neuronal tract in the construction of subsequent complex neuronal circuits that trigger coordinated behavior.
Highlights
During vertebrate development, the central nervous system (CNS) has stereotyped neuronal tracts that include longitudinal and commissural axonal bundles, such as the medial longitudinal fascicle or the posterior commissure (PC)
Our present findings suggest that expression patterns of Slit2 and Robo2 are conserved in tetrapods, and that their signaling contributes to the construction of the PC in Xenopus
Swimming behavior in morpholino antisense oligonucleotides (MO)-treated larvae To study the molecular functions of Xenopus cognates of slit2 (Xlslit2) and robo2 (Xlrobo2) in the developing nervous system, MO were injected into the blastomere, which differentiates into the CNS
Summary
The central nervous system (CNS) has stereotyped neuronal tracts (scaffolds) that include longitudinal and commissural axonal bundles, such as the medial longitudinal fascicle or the posterior commissure (PC). Previous studies have revealed that the interaction between Slit (ligand) and Robo (receptor), which acts as a repulsive guidance signal, plays an essential role in the formation of early scaffolds, e.g., the inhibition of Slit or Robo results in an abnormal morphology of the TPOC [21,22,23] and SOT [24]. These molecules are involved in the formation of commissural tracts in insects [25, 26] and vertebrates (Slit:[27, 28]; Robo:[29, 30]). These results indicate that interaction between Slit and Robo is involved in the construction of the PC and the formation of neuronal element(s) that control coordinated body movement in Xenopus larvae
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