Age-dependent transcriptome and proteome following transection of neonatal spinal cord of Monodelphis domestica (South American grey short-tailed opossum).

Norman R Saunders,C Joakim Ek,Mark D Habgood,Shane A Liddelow,W Dalton Dietrich,Jessie Truettner,A Ian Smith,Katarzyna M Dziegielewska,Benjamin J Wheaton,Helen Lindsay,Natassya M Noor,Matthew J Wakefield,David L Steer,Robert D Miller

doi:10.1371/journal.pone.0099080

Abstract

This study describes a combined transcriptome and proteome analysis of Monodelphis domestica response to spinal cord injury at two different postnatal ages. Previously we showed that complete transection at postnatal day 7 (P7) is followed by profuse axon growth across the lesion with near-normal locomotion and swimming when adult. In contrast, at P28 there is no axon growth across the lesion, the animals exhibit weight-bearing locomotion, but cannot use hind limbs when swimming. Here we examined changes in gene and protein expression in the segment of spinal cord rostral to the lesion at 24 h after transection at P7 and at P28. Following injury at P7 only forty genes changed (all increased expression); most were immune/inflammatory genes. Following injury at P28 many more genes changed their expression and the magnitude of change for some genes was strikingly greater. Again many were associated with the immune/inflammation response. In functional groups known to be inhibitory to regeneration in adult cords the expression changes were generally muted, in some cases opposite to that required to account for neurite inhibition. For example myelin basic protein expression was reduced following injury at P28 both at the gene and protein levels. Only four genes from families with extracellular matrix functions thought to influence neurite outgrowth in adult injured cords showed substantial changes in expression following injury at P28: Olfactomedin 4 (Olfm4, 480 fold compared to controls), matrix metallopeptidase (Mmp1, 104 fold), papilin (Papln, 152 fold) and integrin α4 (Itga4, 57 fold). These data provide a resource for investigation of a priori hypotheses in future studies of mechanisms of spinal cord regeneration in immature animals compared to lack of regeneration at more mature stages.

Highlights

The studies of Aguayo and colleagues in the 1980s [1,2], which repeated an old experiment of Tello [3] using implants and bridges of sciatic nerve to promote regeneration of the central nervous system (CNS) resulted in a concentrated effort to understand the mechanisms underlying the failure of the adult mammalian spinal cord to exhibit regenerative recovery following injury
It is likely that bleeding occurred in some of the postnatal day 7 (P7) injured cords collected for RNA sequencing (RNA-Seq) analysis, but the P28 cords were probably more contaminated, which may account for the presence of upregulated blood-related genes at P28 but not P7 following injury
Note that the gap between the rostral and caudal ends of the transected spinal cord at 24 h post injury was much greater in the P28 (Fig. 1D) cord compared to the P7 cord (Fig. 1C)

Summary

Introduction

The studies of Aguayo and colleagues in the 1980s [1,2], which repeated an old experiment of Tello [3] using implants and bridges of sciatic nerve to promote regeneration of the central nervous system (CNS) resulted in a concentrated effort to understand the mechanisms underlying the failure of the adult mammalian spinal cord to exhibit regenerative recovery following injury. Since several such inhibitory mechanisms have been described including myelin inhibitory factors [4,5] and proteoglycans [6,7,8]. Only one RNA-Seq dataset of injured spinal cord has been published [18] additional information may perhaps be gleaned from an RNA-Seq study that examined the effects of transplanted progenitor/stem cells following spinal cord injury [19]

Methods

Results

Discussion

Conclusion