Sox11 overexpression restores embryonic pro-growth transcription in mature corticospinal tract neurons.

Neurons in the central nervous system (CNS) display a high capacity for axon growth during early development but mostly lose this ability during a key stage of differentiation marked by synaptic maturation, circuit integration, and a profound shift in gene transcription. Once mature, neurons largely fail to reverse this transcriptional switch after axon injury, fundamentally constraining their intrinsic capacity for repair. Here, we show with single-nucleus RNA sequencing that forced expression of the transcription factor Sox11 in adult corticospinal tract neurons produces large-scale and stable changes in gene expression that are highly enriched for growth-relevant processes, and which strongly resemble those of pre-synaptic embryonic stages. Moreover, Sox11 is equally effective when delivered to chronically injured CST neurons. These data reveal Sox11’s ability to reverse a critical step of neuronal maturation even in otherwise unperturbed neurons, clarifying the transcriptional underpinnings and highlighting Sox11’s potential as a pro-regenerative stimulus. In adult mouse samples, corticospinal tract (CST) neurons were transduced with a retrograde, nuclear-localized fluorophore (mGl) and control or Sox11-expressing virus by retrograde transduction from cervical spinal cord. Animals recevied either no injury or a cervical contusion injury six weeks prior to tissue collection. Animals that received Sox11 and no injury were collected at four time points: 1 week, 2 weeks, 4 weeks, or 6 weeks after viral delivery, with each time point uniquely barcoded and pooled in the same sequencing reaction. Embryonic cortex was collected at embryonic day 18. For all samples, single nucleus RNA sequencing was performed. Adult samples were pre-purified using fluorescent activated nuclei sorting prior to library preparation. E18 embryonic libraries were prepared from ixed cortical tissue.