Identification of regenerative processes in neonatal spinal cord injury in the opossum (Monodelphis domestica): A transcriptomic study

• Published in: Journal of comparative neurology (1911) 2021-04, Vol.529 (5), p.969-986
• Main Authors: Wheaton, Benjamin J., Sena, Johnny, Sundararajan, Anitha, Umale, Pooja, Schilkey, Faye, Miller, Robert D.
• Format: Article
• Language: English
• Subjects: Aging - genetics; Aging - physiology; Animals; Animals, Newborn; Apoptosis; Association analysis; axon regeneration; Axonogenesis; Base Sequence; Cell adhesion; Cell adhesion & migration; Cell proliferation; Endothelial cells; Endothelial Cells - metabolism; Gene expression; Gene Expression Regulation, Developmental; Gene Ontology; GO category overrepresentation; gray short‐tailed opossum (Monodelphis domestica); Microglia; Monodelphis - physiology; Monodelphis domestica; Neonates; Nerve Tissue Proteins - biosynthesis; Nerve Tissue Proteins - genetics; Neuroglia - metabolism; Neurons - metabolism; Organ Specificity; Regeneration; Ribonucleic acid; RNA; RNA sequencing; Species Specificity; Spinal Cord - growth & development; Spinal Cord - metabolism; Spinal cord injuries; Spinal Cord Injuries - genetics; Spinal Cord Injuries - physiopathology; spinal cord injury; Spinal Cord Regeneration - physiology; Transcriptome; Transcriptomics
• ISSN: 0021-9967; 1096-9861; 1096-9861
• DOI: 10.1002/cne.24994

This study investigates the response to spinal cord injury in the gray short‐tailed opossum (Monodelphis domestica). In opossums spinal injury early in development results in spontaneous axon growth through the injury, but this regenerative potential diminishes with maturity until it is lost entirely. The mechanisms underlying this regeneration remain unknown. RNA sequencing was used to identify differential gene expression in regenerating (SCI at postnatal Day 7, P7SCI) and nonregenerating (SCI at Day 28, P28SCI) cords +1d, +3d, and +7d after complete spinal transection, compared to age‐matched controls. Genes showing significant differential expression (log2FC ≥ 1, Padj ≤ 0.05) were used for downstream analysis. Across all time‐points 233 genes altered expression after P7SCI, and 472 genes altered expression after P28SCI. One hundred and forty‐seven genes altered expression in both injury ages (63% of P7SCI data set). The majority of changes were gene upregulations. Gene ontology overrepresentation analysis in P7SCI gene‐sets showed significant overrepresentations only in immune‐associated categories, while P28SCI gene‐sets showed overrepresentations in these same immune categories, along with other categories such as “cell proliferation,” “cell adhesion,” and “apoptosis.” Cell‐type–association analysis suggested that, regardless of injury age, injury‐associated gene transcripts were most strongly associated with microglia and endothelial cells, with strikingly fewer astrocyte, oligodendrocyte and neuron‐related genes, the notable exception being a cluster of mostly downregulated oligodendrocyte‐associated genes in the P7SCI + 7d gene‐set. Our findings demonstrate a more complex transcriptomic response in nonregenerating cords, suggesting a strong influence of non‐neuronal cells in the outcome after injury and providing the largest survey yet of the transcriptomic changes occurring after SCI in this model. In opossums, spinal injury early in development results in spontaneous axon growth through the injury, but this regeneration diminishes with maturity until it is lost entirely. Analysis of the postinjury transcriptomes suggests that there is a more complex transcriptomic response in nonregenerating cords, suggesting a stronger influence of non‐neuronal cells in the outcome after injury, and suggesting that a prolonged immune response may be inhibitory to spinal cord regeneration.