Complex interactions amongst N-cadherin, DLAR, and Liprin-alpha regulate Drosophila photoreceptor axon targeting.

The formation of stable adhesive contacts between pre- and post-synaptic neurons represents the initial step in synapse assembly. The cell adhesion molecule N-cadherin, the receptor tyrosine phosphatase DLAR, and the scaffolding molecule Liprin-alpha play critical, evolutionarily conserved roles in this process. However, how these proteins signal to the growth cone and are themselves regulated remains poorly understood.

Activation of Rho after traumatic brain injury and seizure in rats.

Traumatic brain injury (TBI) is characterized by a progressive cell loss and a lack of axonal regeneration. In the central nervous system (CNS), the Rho signaling pathway regulates the neuronal response to growth inhibitory proteins and regeneration of damaged axons, and Rho activation is also correlated with an increased susceptibility to apoptosis. To evaluate whether traumatic brain injury (TBI) results in changes in Rho activation in vulnerable regions of the brain, GTP-RhoA pull down assays were performed on rat cortical and hippocampal tissue homogenates obtained from 24 h to 3 days following lateral fluid percussion brain injury (FPI).

SHP-1 negatively regulates neuronal survival by functioning as a TrkA phosphatase.

Nerve growth factor (NGF) mediates the survival and differentiation of neurons by stimulating the tyrosine kinase activity of the TrkA/NGF receptor. Here, we identify SHP-1 as a phosphotyrosine phosphatase that negatively regulates TrkA. SHP-1 formed complexes with TrkA at Y490, and dephosphorylated it at Y674/675.

Rho activation patterns after spinal cord injury and the role of activated Rho in apoptosis in the central nervous system.

Growth inhibitory proteins in the central nervous system (CNS) block axon growth and regeneration by signaling to Rho, an intracellular GTPase. It is not known how CNS trauma affects the expression and activation of RhoA. Here we detect GTP-bound RhoA in spinal cord homogenates and report that spinal cord injury (SCI) in both rats and mice activates RhoA over 10-fold in the absence of changes in RhoA expression.

Inactivation of intracellular Rho to stimulate axon growth and regeneration.

Our studies indicate that the small GTPase Rho is an important intracellular target for promoting axon regrowth after injury. In tissue culture, inactivation of the Rho signaling pathway is effective in promoting neurite growth on growth inhibitory CNS substrates by two different methods: inactivation of Rho with C3 transferase, and inactivation by dominant negative mutation of Rho. In vivo, we have documented the regeneration of transfected axons after treatment with C3 in two different animals models, microcrush lesion of the adult rat optic nerve, and over-hemisection of adult mouse spinal cord.

Characterization of new cell permeable C3-like proteins that inactivate Rho and stimulate neurite outgrowth on inhibitory substrates.

The activation state of Rho is an important determinant of axon growth and regeneration in neurons. Axons can extend neurites on growth inhibitory substrates when Rho is inactivated by C3-ADP-ribosyltransferase (C3). We found by Rho-GTP pull-down assay that inhibitory substrates activate Rho.