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Open Access Research article

Neuropilin2 regulates the guidance of post-crossing spinal commissural axons in a subtype-specific manner

Tracy S Tran1*, Edward Carlin2, Ruihe Lin1, Edward Martinez1, Jane E Johnson4 and Zaven Kaprielian23*

Author Affiliations

1 Department of Biological Sciences, Rutgers University, Boyden 206, 195 University Ave., Newark, NJ 07102, USA

2 Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Kennedy Center Room 624, 1410 Pelham Parkway South, Bronx, NY 10461, USA

3 Department of Pathology, Albert Einstein College of Medicine, Kennedy Center Room 624, 1410 Pelham Parkway South, Bronx, NY 10461, USA

4 Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas, USA

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Neural Development 2013, 8:15  doi:10.1186/1749-8104-8-15

Published: 31 July 2013

Abstract

Background

Spinal commissural axons represent a model system for deciphering the molecular logic that regulates the guidance of midline-crossing axons in the developing central nervous system (CNS). Whether the same or specific sets of guidance signals control the navigation of molecularly distinct subtypes of these axons remains an open and largely unexplored question. Although it is well established that post-crossing commissural axons alter their responsiveness to midline-associated guidance cues, our understanding of the repulsive mechanisms that drive the post-crossing segments of these axons away from the midline and whether the underlying guidance systems operate in a commissural axon subtype-specific manner, remains fragmentary at best.

Results

Here, we utilize axonally targeted transgenic reporter mice to visualize genetically distinct dorsal interneuron (dI)1 and dI4 commissural axons and show that the repulsive class 3 semaphorin (Sema3) guidance receptor Neuropilin 2 (Npn2), is selectively expressed on the dI1 population and is required for the guidance of post-crossing dI1, but not dI4, axons. Consistent with these observations, the midline-associated Npn2 ligands, Sema3F and Sema3B, promote the collapse of dI1, but not dI4, axon-associated growth cones in vitro. We also identify, for the first time, a discrete GABAergic population of ventral commissural neurons/axons in the embryonic mouse spinal cord that expresses Npn2, and show that Npn2 is required for the proper guidance of their post-crossing axons.

Conclusions

Together, our findings indicate that Npn2 is selectively expressed in distinct populations of commissural neurons in both the dorsal and ventral spinal cord, and suggest that Sema3-Npn2 signaling regulates the guidance of post-crossing commissural axons in a population-specific manner.

Keywords:
Semaphorins; Atoh1; Neurog2; Development; Spinal cord