Neuronal injury affects expression of helix-loop-helix transcription factors.

Helix-loop-helix transcription (HLH) factors regulate several stages of neuronal development including differentiation of individual populations of neurons and neurite growth. Here we demonstrate that axonal injury of corticospinal and dorsal root ganglion neurons induces changes in the expression of several HLH transcription factors that function as negative regulators of neurogenesis and neurite outgrowth. However, the expression of HLH transcription factors that stimulate neurogenesis is not affected by the axonal injury. Expression of HES, SHARP and Id family members is suppressed shortly after axonal injury and expression returns to normal levels after 14 days. We hypothesize that down-regulation of these HLH transcription factors is required for initiation of regenerative response to axonal injury.