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  • The tumor suppressor HHEX inhibits axon growth when prematurely expressed in developing central nervous system neurons.

The tumor suppressor HHEX inhibits axon growth when prematurely expressed in developing central nervous system neurons.

Molecular and cellular neurosciences (2015-08-27)
Matthew T Simpson, Ishwariya Venkatesh, Ben L Callif, Laura K Thiel, Denise M Coley, Kristen N Winsor, Zimei Wang, Audra A Kramer, Jessica K Lerch, Murray G Blackmore
ABSTRACT

Neurons in the embryonic and peripheral nervous system respond to injury by activating transcriptional programs supportive of axon growth, ultimately resulting in functional recovery. In contrast, neurons in the adult central nervous system (CNS) possess a limited capacity to regenerate axons after injury, fundamentally constraining repair. Activating pro-regenerative gene expression in CNS neurons is a promising therapeutic approach, but progress is hampered by incomplete knowledge of the relevant transcription factors. An emerging hypothesis is that factors implicated in cellular growth and motility outside the nervous system may also control axon growth in neurons. We therefore tested sixty-nine transcription factors, previously identified as possessing tumor suppressive or oncogenic properties in non-neuronal cells, in assays of neurite outgrowth. This screen identified YAP1 and E2F1 as enhancers of neurite outgrowth, and PITX1, RBM14, ZBTB16, and HHEX as inhibitors. Follow-up experiments are focused on the tumor suppressor HHEX, one of the strongest growth inhibitors. HHEX is widely expressed in adult CNS neurons, including corticospinal tract neurons after spinal injury, but is present only in trace amounts in immature cortical neurons and adult peripheral neurons. HHEX overexpression in early postnatal cortical neurons reduced both initial axonogenesis and the rate of axon elongation, and domain deletion analysis strongly implicated transcriptional repression as the underlying mechanism. These findings suggest a role for HHEX in restricting axon growth in the developing CNS, and substantiate the hypothesis that previously identified oncogenes and tumor suppressors can play conserved roles in axon extension.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Monoclonal Anti-HHEX antibody produced in mouse, clone 1A5, purified immunoglobulin, buffered aqueous solution
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Anti-Microtubule-Associated Protein 2 (MAP2) Antibody, Chemicon®, from rabbit
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Anti-Tau-1 Antibody, clone PC1C6, clone PC1C6, Chemicon®, from mouse
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Anti-β-Tubulin III antibody produced in rabbit, affinity isolated antibody, buffered aqueous solution
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Poly-D-lysine hydrobromide, mol wt 30,000-70,000
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Forskolin, from Coleus forskohlii, ≥98% (HPLC), powder
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Anti-NeuN Antibody, clone A60, Alexa Fluor 555 Conjugate, clone A60, from mouse, ALEXA FLUOR 555