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Chromatin states at homeoprotein loci distinguish axolotl limb segments prior to regeneration [RNA-seq]

ABSTRACT: The salamander limb regenerates only the missing portion. Each limb segment can only form segments equivalent to- or more distal to their own identity, relying on a property termed “positional information”. How positional information is encoded in limb cells has been unknown. By cell-type-specific chromatin profiling of upper arm, lower arm, and hand, we found segment-specific levels of histone H3K27me3 at limb homeoprotein gene loci but not their upstream regulators, constituting an intrinsic segment information code. During regeneration, regeneration-specific regulatory elements became active prior to the re-appearance of developmental regulatory elements. This means that, in the hand segment, the permissive chromatin state of the hand homeoprotein gene HoxA13 engages with regeneration regulatory elements, bypassing the upper limb program. We performed Differential Gene expression analysis using data obtained from RNA-seq of two mature limb segments (mature arm vs hand). Therefore, we performed libraries from the mature arm and 5, 9, 13 dpa regenerating arm blastema.

ORGANISM(S): Ambystoma mexicanum

PROVIDER: GSE217593 | GEO | 2023/04/10

REPOSITORIES: GEO

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Chromatin states at homeoprotein loci distinguish axolotl limb segments prior to regeneration [ATAC-seq]

Project description:The salamander limb regenerates only the missing portion. Each limb segment can only form segments equivalent to- or more distal to their own identity, relying on a property termed “positional information”. How positional information is encoded in limb cells has been unknown. By cell-type-specific chromatin profiling of upper arm, lower arm, and hand, we found segment-specific levels of histone H3K27me3 at limb homeoprotein gene loci but not their upstream regulators, constituting an intrinsic segment information code. During regeneration, regeneration-specific regulatory elements became active prior to the re-appearance of developmental regulatory elements. This means that, in the hand segment, the permissive chromatin state of the hand homeoprotein gene HoxA13 engages with regeneration regulatory elements, bypassing the upper limb program. Profiling chromatin accessibility (ACRs) of Axoltol limb connective tissue cells, and compare among developmental limb buds, and mature limb at different segments and regeneration time points.

2023-04-10 | GSE217592 | GEO

Chromatin states at homeoprotein loci distinguish axolotl limb segments prior to regeneration [Cut&Tag]

Project description:The salamander limb regenerates only the missing portion. Each limb segment can only form segments equivalent to- or more distal to their own identity, relying on a property termed “positional information”. How positional information is encoded in limb cells has been unknown. By cell-type-specific chromatin profiling of upper arm, lower arm, and hand, we found segment-specific levels of histone H3K27me3 at limb homeoprotein gene loci but not their upstream regulators, constituting an intrinsic segment information code. During regeneration, regeneration-specific regulatory elements became active prior to the re-appearance of developmental regulatory elements. This means that, in the hand segment, the permissive chromatin state of the hand homeoprotein gene HoxA13 engages with regeneration regulatory elements, bypassing the upper limb program. Profiling histone marks of Axoltol limb connective tissue cells, and comparing among limb different limb segments and mature vs regeneration time points.

2023-04-10 | GSE217591 | GEO

Retinoic acid breakdown is required for proximodistal positional identity during axolotl limb regeneration

Project description:Regenerating limbs retain their proximodistal (PD) positional identity following amputation. This positional identity is encoded genetically by PD patterning genes, which instruct blastema cells to regenerate the appropriate PD limb segment. Retinoic acid (RA) is known to specify proximal limb identity, but how RA concentration is established in the blastema is unknown. Here, we show that RA breakdown via CYP26B1 is essential for determining the RA concentration within blastemas. CYP26B1 inhibition molecularly reprograms distal blastemas into a proximal identity, phenocopying the effects of administering excess RA. We identify Shox as an RA responsive gene that is differentially expressed between proximally and distally amputated blastemas. Ablation of Shox results in shortened limbs with proximal skeletal elements that fail to undergo endochondral ossification. These results suggest that PD positional identity is determined by RA degradation and that targets of RA have a critical role in skeletal element formation during limb regeneration.

2024-07-22 | GSE272731 | GEO

Retinoic acid receptors and the control of positional information in the regenerating axolotl limb

Project description:We know little about the control of positional information (PI) during axolotl limb regeneration which ensures that the limb regenerates exactly what was amputated and the work reported here investigates this phenomenon. Retinoic acid administration changes the PI in a proximal direction so that a complete limb can be regenerated from a hand. Rather that identifying all the genes altered by RA treatment of the limb, we have eliminated many off-target effects by using retinoic acid receptor selective agonists. We firstly identify the receptor involved in this respecification process as RARα and secondly identify the genes involved by RNA sequencing of the RARα-treated blastemal mesenchyme. We find 1177 up-regulated genes and 1403 down-regulated genes which could be identified using the axolotl genome. These include several genes known to be involved in retinoic acid metabolism and in patterning. Since positional in-formation is thought to be a property of the cell surface of blastemal cells when we examine our dataset with an emphasis on this aspect, we find the top canonical pathway is integrin signaling. In the extracellular matrix compartment, we find an MMP and several collagens are up-regulated and several cell membrane genes and secretory factors are also up-regulated. This provides data for future testing of the function of these candidates in the control of PI during limb regeneration.

2021-08-20 | GSE182296 | GEO

Positional information modulates transient regeneration-activated cell states during vertebrate appendage regeneration.

Project description:Positional information modulates transient regeneration-activated cell states during vertebrate appendage regeneration.

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Single-cell analysis uncovers convergence of cell identities during axolotl limb regeneration

Project description:Amputation of the axolotl forelimb results in the formation of a blastema, a transient tissue where progenitor cells accumulate prior to limb regeneration. Connective tissue (CT) – skeleton, periskeleton, tendon, dermis, interstitial cells – contributes the vast majority of cells that populate the blastema, however it is unclear how individual CT cells may reprogram their fate in order to rebuild the tetrapod limb. Here we use a combination of Cre-loxP reporter lineage tracking and single-cell (sc) RNA-seq to molecularly track, for the first time, adult CT cell heterogeneity and its transition to a limb blastema state. We uncover a multi-phasic molecular program where CT cell types found in the uninjured adult limb revert to a relatively homogenous progenitor state that participates in inflammation and extracellular matrix disassembly prior to proliferation, establishment of positional information, and ultimately re-differentiation. While the early regeneration transcriptome states are unique to the blastema, the later stages recapitulate embryonic limb development. Notably, we do not find evidence of a pre-existing blastema-like precursor nor limb bud-like progenitors in the uninjured adult tissue. However, we find that distinct CT subpopulations in the adult limb differentially contribute to proximal and distal portions of the regenerated limb. Together, our data illuminates molecular and cellular reprogramming during complex organ regeneration in a vertebrate.

2018-09-27 | GSE106269 | GEO

Comparative Transcriptional Profiling of the Axolotl Limb Identifies a Tripartite Regeneration-Specific Gene Program

Project description:Identifying the genetic program that induces limb regeneration in salamanders is an important resource for regenerative medicine, which currently lacks tools to promote regeneration of functional body structures. The genetic network underlying limb regeneration has been elusive due to the complexity of the injury response that occurs concomitant to blastema formation. Here we performed parallel expression profile time courses of non-regenerative lateral wounds versus amputated limbs in axolotl. We show that limb regeneration occurs in three distinguishable phases--early wound healing followed by a transition phase leading to establishment of the limb development program. By focusing on the transition phase, we identified 93 strictly regeneration-associated genes involved in oxidative stress response, chromatin modification, epithelial development and limb development. The specific expression of the genes was confirmed by in situ hybridization. Regeneration-specific expression databases are critical resources for understanding how regeneration-relevant phenotypes can be induced from adult cells Regeneration of the axolotl forelimb lower arm was compared with the healing of a deep lateral injury in a high density timecourse (uncut, 3h, 6h, 9h, 12h, 24h, 36h, 52h, 72h, 120h, 168h, 288h and 528h after injury). Three independent biological replicates were performed using separate cluches of animals. Amputated and lateral wound samples were made as matched contralateral samples of four pooled animals per timepoint.

2013-01-01 | E-GEOD-36451 | biostudies-arrayexpress

Positional information modulates transient regeneration-activated cell states during vertebrate appendage regeneration.

Project description:Injury is a common occurrence in the life of most if not all organisms. Because injury and the extent of damage inflicted are not predictable events, pre-existing tissues must somehow determine how much tissue needs to be restored. It has been known for over a century that amputation position along a proximal-distal (P/D) axis determines the regeneration speed of amputated limbs in regeneration-competent animals1. Yet, it is not clear how an injured limb conveys positional information during regeneration to faithfully restore pre-existing morphologies and functions. Here, we profiled millimetric caudal fins regenerating proximal and distal amputations in the African killifish (Nothobranchius furzeri). We report position-specific, differential modulation of the spatial distribution, duration, and magnitude of proliferation, and the possibility to predict blastema sizes. Regenerating fins profiled by single cell RNA sequencing identified a Transient Regeneration-Activated Cell State (TRACS) enriched in extracellular matrix (ECM) components and modifiers that is proportionally amplified to match a given amputation position. We located this transient cell state to the basal epidermis by gene expression and confocal microscopy, and propose a role for these cells in transducing positional information to the regeneration blastema. Understanding the temporal deployment of regenerative cell states may hold the key to set up a successful regeneration event in organisms with limited regenerative abilities such as humans.

2024-04-01 | GSE260629 | GEO

Chromatin states at homeoprotein loci distinguish axolotl limb segments prior to regeneration

Project description:Chromatin states at homeoprotein loci distinguish axolotl limb segments prior to regeneration

| PRJNA899785 | ENA

Tig1 regulates proximo-distal identity during salamander limb regeneration

Project description:Salamander limb regeneration is an accurate process which gives rise exclusively to the missing structures, irrespective of the amputation level. This suggests that cells in the stump have an awareness of their spatial location, a property termed ‘positional identity’. Little is known about how positional identity is encoded, in salamanders or other biological systems. Through single-cell RNAseq analysis, we identified Tig1/RARRES1 as a potential determinant of proximal identity. Tig1 encodes a conserved cell surface molecule, is regulated by retinoic acid and exhibits a graded expression along the proximo-distal axis of the limb. Its overexpression leads to regeneration defects in the distal elements and elicits proximal displacement of blastema cells, while its neutralisation blocks proximo-distal cell surface interactions. Critically, Tig1 reprogrammes distal cells to a proximal identity, upregulating Prod1 and inhibiting HoxA13 and distal transcriptional networks. Thus, Tig1 is a central cell surface determinant of proximal identity in the salamander limb.

2022-01-30 | GSE184948 | GEO

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