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Systemic stem cell activation following amputation primes distant appendages for future regeneration events in axolotl

ABSTRACT: A remarkable diversity in regenerative competency of extant species suggests an evolutionary influence, but few studies have identified potential selective pressures shaping this variation. Uncovering these selective pressures is critical to understanding the key molecular similarities, and differences, between regeneratorsand non-regenerators. Here we report that, in the highly-regenerative axolotl, an evolutionarily conserved body-wide stem cell activation response primes other limbs for faster regeneration, offering a selective advantage for this phenomenon. We further demonstrate the body-wide response requires peripheral nervous system input at these distant sites and is predicated on mTOR signaling. We definedgene expression changes within the signaling neural processes and nearby tissues, harboring responsive stem cells, leading to candidate genetic pathways central to this process. Functional experimentation confirmed a requirement for adrenergic signaling in amputation-induced activation of distant stem cells. Our study provides a direct link between body-wide cellular activation responses and regeneration, unifying previous reports from distant species of various natural regenerative abilities, such as planarians and mice, in a conceptual framework that centers the ability to convert the body-wide response to local tissue outgrowth as the key difference between regenerators and non-regenerators.

ORGANISM(S): Ambystoma mexicanum

PROVIDER: GSE192477 | GEO | 2022/01/01

REPOSITORIES: GEO

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Project description:Variability of regenerative potential among animals has long perplexed biologists. Based on their amazing regenerative abilities, planarians have become important models for understanding the molecular basis of regeneration; however, planarian species with limited regenerative abilities are also found. Despite the importance of understanding the differences between closely related, regenerating and non-regenerating organisms, few studies have focused on the evolutionary loss of regeneration, and the molecular mechanisms leading to such regenerative loss remain obscure. Here we examine Procotyla fluviatilis, a planarian with restricted ability to replace missing tissues, utilizing next-generation sequencing to define the gene expression programs active in regeneration-permissive and regeneration-deficient tissues. We found that Wnt signaling is aberrantly activated in regeneration-deficient tissues. Remarkably, down-regulation of canonical Wnt signaling in regeneration-deficient regions restores regenerative abilities: blastemas form and new heads regenerate in tissues that normally never regenerate. This work reveals that manipulating a single signaling pathway can reverse the evolutionary loss of regenerative potential. RNA-seq experiments to identify gene expression changes following amputation in body regions with variable regenerative potential. Adult Procotyla fluviatilis were amputated at sites either anterior or posterior to the pharynx. After 24 hours post-amputation, tissues near the amputation site were excised and RNA was extracted. Similar tissues were excised from uncut control animals. Samples were processed for RNA-seq using Illumina procedures. We generated a de novo P. fluviatilis transcriptome and used RNA sequencing (RNA-seq) to characterize transcripts from excised tissue fragments in Reg+ and Reg- body regions 24 hours post-amputation. We performed parallel analyses on tissues excised from intact animals at identical body regions to account for regional differences in transcripts, thereby identifying changes resulting from amputation. Samples A1-A3 = Regeneration-proficient (Reg+) tissue excision 24 hours after amputation. Samples B1-B3 = Tissue excision from regeneration-proficient (Reg+) region but not amputated. Samples C1-C3 = Tissue excision from regeneration-deficient (Reg-) tissues 24 hours after amputation. Samples D1, D3-D4 = Tissue excision from regeneration-deficient (Reg-) region that was not amputated.

Project description:Retinal Müller glia (MG) can act as stem-like cells to generate new neurons in both zebrafish in mice. In zebrafish, retinal regeneration is innate and robust, resulting in the replacement of lost neurons and restoration of visual function. In mice, exogenous stimulation of MG is required to reveal a dormant and, to date, limited regenerative capacity. Zebrafish studies have been key in revealing factors that promote regenerative responses in the mammalian eye. Increased understanding of how the regenerative potential of MG is regulated in zebrafish may therefore aid efforts to promote retinal repair therapeutically. Developmental signaling pathways are known to coordinate regeneration following widespread retinal cell loss. In contrast, less is known about how regeneration is regulated in the context of retinal degenerative disease, i.e., following the loss of specific retinal cell types. To address this knowledge gap, we compared transcriptomic changes between two selective cell ablation paradigms, targeted loss of rod photoreceptors or bipolar cells. Our study spanned twelve time points encompassing the entire degenerative and regenerative process of each targeted cell type. 2,531 differentially expressed genes (DEGs) were identified. Interestingly, the majority of DEGs were paradigm specific, including during MG activation phases, suggesting the nature of the injury/cell loss informs the regenerative process from initiation onward. For example, early modulation of Notch signaling was implicated in the rod but not bipolar cell ablation paradigm. Components of JAK/STAT signaling were activated in both paradigms but were more strongly induced during rod cell regeneration. We functionally validated the role of JAK/STAT signaling during rod cell regeneration using CRISPR/Cas9-based knockdown of stat3 which inhibited both MG proliferation and rod cell regeneration kinetics. Additionally, although more than a third of all DEGs are implicated as immune-system regulators, individual immune-related factors were largely paradigm specific. These data support emerging evidence that discrete “fate-biased” regenerative processes follow from selective retinal cell loss. Microarrays were used to follow gene expression changes in the eyes of fish following either rod or bipolar specific induced death.

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Systemic stem cell activation following amputation primes distant appendages for future regeneration events in axolotl

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