Project description:Tissue regeneration is associated with complex changes in gene expression and post-translational modifications of proteins, including transcription factors and histones that comprise chromatin. We tested 173 compounds designed to target epigenetic mechanisms in an axolotl (Ambystoma mexicanum) embryo tail regeneration assay. A relatively large number of compounds (N = 31) reproducibly inhibited tail regeneration, including multiple histone deacetylase inhibitors (HDACi). In particular, romidepsin potently inhibited tail regeneration when embryos were treated continuously for 7 days. Additional experiments revealed that romidepsin acts within a very narrow, post-injury window. Romidepsin treatment for only 1 minute post-amputation inhibited regeneration through the first 7 days, however after this time, regeneration commenced with variable outgrowth of tailfin tissue and abnormal patterning. Microarray analysis showed that romidepsin altered early, transcriptional responses at 3 and 6-hour post-amputation, especially targeting genes that function in the regulation of transcription, cell differentiation, cell proliferation, pattern specification, and tissue morphogenesis. Our results show that HDAC activity is required at the time of tail amputation to regulate the initial transcriptional response to injury and regeneration.
Project description:The Mexican axolotl provides a powerful model to investigate mechanisms of tissue regeneration. A recent chemical screen found that HDAC inhibitor romidepsin, administered for only 1-minute post amputation (1 MPA), blocks axolotl tail regeneration. Here, we tested the potential for cobalt chloride (CoCl2), a chemical stabilizer of HIF1a and inducer of hypoxia, to rescue romidepsin-inhibition of tail regeneration. Tail regeneration was partially rescued when embryos with amputated tails were co-treated with romidepsin and CoCl2. However, extending the CoCl2 dosage window either inhibited regeneration (CoCl2:0-30 MPA) or was lethal (CoCl2:0-24 hours post amputation; HPA). CoCl2:0-30 MPA caused tissue damage, tissue loss, and cell death at the distal tail tip, and blocked regeneration. In contrast, CoCl2 treatment of non-amputated embryos or CoCl2:60-90 MPA treatment of amputated embryos did not affect wound healing or inhibit tail regeneration. To further investigate the contrasting effects of CoCl2, microarray analysis was performed to identify differentially expressed genes at 3 HPA. CoCl2-romidepsin:1 MPA treatment significantly increased the expression of transcription factors associated with appendage regeneration, while CoCl2:0-30 MPA significantly increased expression of hemoglobin and platelet-specific transcripts, consistent with hemorrhage and an impaired hemostatic response. Also, CoCl2:0-30 MPA significantly increased expression of hypoxia inducible genes, including genes that encode Hif1a interacting proteins and heat shock proteins (HSP); in contrast, genes encoding TGFB signaling components were significantly downregulated. Using additional chemical inhibitors of tail regeneration, we identified transcriptional responses associated with HSP90 activity and TGFB signaling. Notably, geldanamcin decreased transcription of matrix metalloproteinases and sustained muscle-specific gene expression, suggesting a role for HSP90 in regulating extracellular matrix remodeling and muscle dedifferentiation. Our study shows the power of using chemical tools to precisely identify temporal windows within which critical biological processes are enacted during tissue regeneration.
Project description:The Mexican axolotl (Ambystoma mexicanum) is one member of a select group of vertebrate animals that has retained the amazing ability to regenerate multiple body parts. In addition to being an important model system for regeneration, the axolotl is also a leading model system for developmental biologists. Many genes used in development have been identified to be reused again during regeneration, however how this molecular circuitry is controlled during regeneration is unknown. In recent years microRNAs have been identified as key regulators of gene expression during development, in many diseases and also in regeneration. Here we have used deep sequencing combined with qRT-PCR to identify microRNAs that are involved in regulating regeneration in axolotl. This approach has enabled us to identify well known families of microRNAs and in addition to identify putative novel microRNAs that differentially regulated in the regenerating tissue. These findings suggest that microRNAs may play key roles in managing the spatial and temporal expression of genes important for ensuring that the correct tissues are regenerated. small RNA Sequencing (2 samples) in Ambystoma Mexicanum
Project description:The Mexican axolotl (Ambystoma mexicanum) is one member of a select group of vertebrate animals that has retained the amazing ability to regenerate multiple body parts. In addition to being an important model system for regeneration, the axolotl is also a leading model system for developmental biologists. Many genes used in development have been identified to be reused again during regeneration, however how this molecular circuitry is controlled during regeneration is unknown. In recent years microRNAs have been identified as key regulators of gene expression during development, in many diseases and also in regeneration. Here we have used deep sequencing combined with qRT-PCR to identify microRNAs that are involved in regulating regeneration in axolotl. This approach has enabled us to identify well known families of microRNAs and in addition to identify putative novel microRNAs that differentially regulated in the regenerating tissue. These findings suggest that microRNAs may play key roles in managing the spatial and temporal expression of genes important for ensuring that the correct tissues are regenerated.
Project description:Previous studies of appendage regeneration in the axolotl have shown that multiple genetic programs are modulated through regulatory factors. MicroRNAs are short highly conserved non-coding genes that suppress expression of target genes and thereby control multiple genetic programs. Given their important regulatory roles and evolutionary conservation, we hypothesize that microRNAs define a conserved genetic regulatory circuit important for appendage regeneration. We characterized microRNA expression during Axolotl forelimb regeneration using small RNA sequencing. The same samples were assayed for mRNA expression using mRNA sequencing. Small RNA and mRNA gene expression profiling during 0, 3, 6 and 14 days post amputation.
Project description:Humans and other tetrapods are considered to require apical-ectodermal-ridge, AER, cells for limb development, and AER-like cells are suggested to be re-formed to initiate limb regeneration. Paradoxically, the presence of AER in the axolotl, the primary regeneration model organism, remains controversial. Here, by leveraging a single-cell transcriptomics-based multi-species atlas, composed of axolotl, human, mouse, chicken, and frog cells, we first established that axolotls contain cells with AER characteristics. Surprisingly, further analyses and spatial transcriptomics revealed that axolotl limbs do not fully re-form AER cells during regeneration. Moreover, the axolotl mesoderm displays part of the AER machinery, revealing a novel program for limb (re)growth. These results clarify the debate about the axolotl AER and the extent to which the limb developmental program is recapitulated during regeneration.