The Stress Response of the Holothurian Central Nervous System: A Transcriptomic Analysis

Abstract

Injury to the central nervous system (CNS) results in permanent damage and lack of function in most vertebrate animals, due to their limited regenerative capacities. In contrast, echinoderms can fully regenerate their radial nerve cord (RNC) following transection, with little to no scarring. Investigators have associated the regenerative capacity of some organisms to the stress response and inflammation produced by the injury. Here, we explore the gene activation profile of the stressed holothurian CNS. To do this, we performed RNA sequencing on isolated RNC explants submitted to the stress of transection and enzyme dissection and compared them with explants kept in culture for 3 days following dissection. We describe stress-associated genes, including members of heat-shock families, ubiquitin-related pathways, transposons, and apoptosis that were differentially expressed. Surprisingly, the stress response does not induce apoptosis in this system. Other genes associated with stress in other animal models, such as hero proteins and those associated with the integrated stress response, were not found to be differentially expressed either. Our results provide a new viewpoint on the stress response in the nervous system of an organism with amazing regenerative capacities. This is the first step in deciphering the molecular processes that allow echinoderms to undergo fully functional CNS regeneration, and also provides a comparative view of the stress response in other organisms.

Keywords: RNA-seq; echinoderm; heat shock proteins; regeneration; spinal cord injury; ubiquitin.

Figure 1

MA plot of genes in the holothurian CNS. Each point in the plot represents an individual gene. Points colored red represent upregulated genes (log₂ Fold Change ≥ 2 and FDR-adjusted p-value < 0.05), whereas points colored blue represent downregulated genes (log₂ Fold Change ≤ −2 and FDR-adjusted p-value < 0.05).

Figure 2

Bar plots showing top ten enriched functional terms for upregulated genes (A) and downregulated genes (B) at 24 h post-collagenase treatment.

Figure 3

Alignment of Hsp90 homolog identified in the RNC transcriptome with a Hsp90 sequence from A. japonicus.

Figure 4

Alignment of the conserved domains of the Hsp70 homologs identified in the RNC transcriptome.

Figure 5

Alignment of the translated ORFs of the four distinct transcripts from the H. glaberrima RNC transcriptome that matched ubiquitin.

Figure 6

Micrographs of RNC explants at 3 days post-collagenase treatment (A) and 24 h post-collagenase treatment (B). Cell nuclei were stained with DAPI (red), and apoptotic cells were detected using TUNEL (green). Finally, the percentages of apoptotic cells in RNC explants placed in culture for 24 h and 3 d were calculated (C).