A long-term goal of this research is to elucidate the molecular mechanisms controlling contact-dependent axon guidance in the developing mammalian central nervous system (CNS). The ventral midline/floor plate of the rodent CNS represents an important intermediate target for pathfinding of commissural axons. Commissural axons are directed along a circumferential path from the dorsolateral spinal cord to the floor plate by long-range diffusible guidance cues. Short-range cues mediate contact-dependent interactions between commissural growth cones and floor plate cells that allow commissural axons to cross the midline and turn rostrally to form the longitudinally projecting ventral funiculus. Strikingly, these axons appear to ignore guidance cues present on the ipsilateral, but not the contralateral side of the spinal cord, since they turn into the longitudinal plane only after crossing the midline, and do not recross the midline. One interpretation of these observations is that commissural axons become responsive to an unidentified midline repellent only after they cross the midline. Receptor protein tyrosine kinases (RPTKs) of the Eph class are attractive candidates for participating in short-range guidance events at the midline since they interact exclusively with membrane-associated ligands or ephrins, and exhibit dynamic, spatially-restricted expression patterns in the developing CNS. Furthermore, transmembrane B-class ephrins mediate repulsive axon guidance in vitro. We have shown by in situ hybridization that all three B-class ephrins are localized to the floor plate, and that the B-class Eph receptor, EphB1, is likely to be expressed by commissural neurons in the developing mouse spinal cord. Strikingly, EphB1 protein is present on commissural axons only after they cross the ventral midline. Furthermore, preliminary studies demonstrate that B-class ephrins promote the collapse of, and repel, commissural growth cones/axons in vitro. These findings suggest that commissural axons specifically upregulate the expression of EphB1 after crossing the floor plate, and gain responsiveness to inhibitory B-class ephrins at the ventral midline. To test this hypothesis, the stripe/choice assay will be used to determine whether floor plate contact alters the responsiveness of commissural axons/growth cones to B-class ephrins in vitro. A novel spinal cord explant culture system will also be used to determine whether blockade of interactions between B-class ephrins and EphB1 leads to commissural axon recrossing of the ventral midline. Furthermore, ephrin-B3 null mice will be examined for defects in commissure formation in the developing spinal cord and brain.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
1R01NS038505-01A1
Application #
6130624
Study Section
Special Emphasis Panel (ZRG1-MDCN-7 (01))
Program Officer
Finkelstein, Robert
Project Start
2000-04-15
Project End
2003-03-31
Budget Start
2000-04-15
Budget End
2001-03-31
Support Year
1
Fiscal Year
2000
Total Cost
$209,375
Indirect Cost
Name
Albert Einstein College of Medicine
Department
Pathology
Type
Schools of Medicine
DUNS #
009095365
City
Bronx
State
NY
Country
United States
Zip Code
10461
Tran, Tracy S; Carlin, Edward; Lin, Ruihe et al. (2013) Neuropilin2 regulates the guidance of post-crossing spinal commissural axons in a subtype-specific manner. Neural Dev 8:15
Sakai, Nozomi; Insolera, Ryan; Sillitoe, Roy V et al. (2012) Axon sorting within the spinal cord marginal zone via Robo-mediated inhibition of N-cadherin controls spinocerebellar tract formation. J Neurosci 32:15377-87
Bravo-Ambrosio, Arlene; Mastick, Grant; Kaprielian, Zaven (2012) Motor axon exit from the mammalian spinal cord is controlled by the homeodomain protein Nkx2.9 via Robo-Slit signaling. Development 139:1435-46
Bravo-Ambrosio, Arlene; Kaprielian, Zaven (2011) Crossing the border: molecular control of motor axon exit. Int J Mol Sci 12:8539-61
Aguirre-Chen, Cristina; B├╝low, Hannes E; Kaprielian, Zaven (2011) C. elegans bicd-1, homolog of the Drosophila dynein accessory factor Bicaudal D, regulates the branching of PVD sensory neuron dendrites. Development 138:507-18
Reeber, Stacey L; Sakai, Nozomi; Nakada, Yuji et al. (2008) Manipulating Robo expression in vivo perturbs commissural axon pathfinding in the chick spinal cord. J Neurosci 28:8698-708
Kadison, Stephanie R; Murakami, Fujio; Matise, Michael P et al. (2006) The role of floor plate contact in the elaboration of contralateral commissural projections within the embryonic mouse spinal cord. Dev Biol 296:499-513
Jevince, Angela R; Kadison, Stephanie R; Pittman, Andrew J et al. (2006) Distribution of EphB receptors and ephrin-B1 in the developing vertebrate spinal cord. J Comp Neurol 497:734-50
Kadison, Stephanie R; Makinen, Taija; Klein, Rudiger et al. (2006) EphB receptors and ephrin-B3 regulate axon guidance at the ventral midline of the embryonic mouse spinal cord. J Neurosci 26:8909-14
Kadison, Stephanie Rebecca; Kaprielian, Zaven (2004) Diversity of contralateral commissural projections in the embryonic rodent spinal cord. J Comp Neurol 472:411-22

Showing the most recent 10 out of 12 publications