A transcription-dependent switch controls competence of adult neurons for distinct modes of axon growth

DS Smith, JHP Skene - Journal of Neuroscience, 1997 - Soc Neuroscience
Journal of Neuroscience, 1997Soc Neuroscience
Although maturing neurons undergo a precipitous decline in the expression of genes
associated with developmental axon growth, structural changes in axon arbors occur in the
adult nervous system under both normal and pathological conditions. Furthermore, some
neurons support extensive regrowth of long axons after nerve injury. Analysis of adult dorsal
root ganglion (DRG) neurons in culture now shows that competence for distinct types of
axon growth depends on different patterns of gene expression. In the absence of ongoing …
Although maturing neurons undergo a precipitous decline in the expression of genes associated with developmental axon growth, structural changes in axon arbors occur in the adult nervous system under both normal and pathological conditions. Furthermore, some neurons support extensive regrowth of long axons after nerve injury. Analysis of adult dorsal root ganglion (DRG) neurons in culture now shows that competence for distinct types of axon growth depends on different patterns of gene expression. In the absence of ongoing transcription, newly isolated neurons can extend compact, highly branched arbors during the first day in culture. Neurons subjected to peripheral axon injury 2–7 d before plating support a distinct mode of growth characterized by rapid extension of long, sparsely branched axons. A transition from “arborizing” to “elongating” growth occurs in naive adult neurons after ∼24 hr in culture but requires a discrete period of new transcription after removal of the ganglia from the intact animal. Thus, peripheral axotomy—by nerve crush or during removal of DRGs—induces a transcription-dependent change that alters the type of axon growth that can be executed by these adult neurons. This transition appears to be triggered, in large part, by interruption of retrogradely transported signals, because blocking axonal transportin vivo can elicit competence for elongating growth in many DRG neurons. In contrast to peripheral axotomy, interruption of the centrally projecting axons of DRG neurons in vivoleads to subsequent growth in vitro that is intermediate between “arborizing” and “elongating” growth. This suggests that the transition between these two modes of growth is a multistep process and that individual steps may be regulated separately. These observations together suggest that structural remodeling in the adult nervous system need not involve the same molecular apparatus as long axon growth during development and regeneration.
Soc Neuroscience