Retinoic acid signaling controls the formation, proliferation and survival of the blastema during adult zebrafish fin regeneration

Abstract

SUMMARYAdult teleosts rebuild amputated fins through a proliferation-dependent process called epimorphic regeneration, in which a blastema of cycling progenitor cells replaces the lost fin tissue. The genetic networks that control formation of blastema cells from formerly quiescent stump tissue and subsequent blastema function are still poorly understood. Here, we investigated the cellular and molecular consequences of genetically interfering with retinoic acid (RA) signaling for the formation of the zebrafish blastema. We show that RA signaling is upregulated within the first few hours after fin amputation in the stump mesenchyme, where it controls Fgf, Wnt/-catenin and Igf signaling. Genetic inhibition of the RA pathway at this stage blocks blastema formation by inhibiting cell cycle entry of stump cells and impairs the formation of the basal epidermal layer, a signaling center in the wound epidermis. In the established blastema, RA signaling remains active to ensure the survival of the highly proliferative blastemal population by controlling expression of the anti-apoptotic factor bcl2. In addition, RA signaling maintains blastema proliferation through the activation of growth-stimulatory signals mediated by Fgf and Wnt/-catenin signaling, as well as by reducing signaling through the growth-inhibitory non-canonical Wnt pathway. The endogenous roles of RA in adult vertebrate appendage regeneration are uncovered here for the first time. They provide a mechanistic framework to understand previous observations in salamanders that link endogenous sources of RA to the regeneration process itself and support the hypothesis that the RA signaling pathway is an essential component of vertebrate tissue regeneration.

Transcriptomic, proteomic, and metabolomic landscape of positional memory in the caudal fin of zebrafish

“…This difference may be due to genetic or morphological differences among species. However, RA signaling is important for fin development and regeneration (67)(68)(69)(70). We identified several members of the RA signaling pathway with opposing patterns of differential expression along the proximodistal axis of uninjured fins.…”

Inducible genetic system for the axolotl

“…Understanding how salamanders regenerate limbs should provide critical insight into efforts to stimulate these processes in vertebrates that do not regenerate limbs, yet the list of modern molecular genetic tools that can be applied to salamanders is currently very short. Other model systems with a much more sophisticated experimental toolkit, such as zebrafish, have provided valuable clues to the molecular underpinnings of vertebrate appendage regeneration (2)(3)(4)(5)(6)(7)(8)(9)(10)(11). However, fin regeneration in teleost fish (such as zebrafish) is not completely analogous to limb development or regeneration.…”

Molecular mechanisms of reversing neural degeneration by retinoic acid, a major derivative of vitamin A

“…Epimorphic regeneration is a well-known phenomenon among male teleosts fish and among many amphibians (Mathew et al, 2009;Blum and Begemann, 2012;Zakany et al, 2004). The RA signaling has been well studied in fin regeneration of zebrafish (Blum and Begemann, 2012).…”

“…The RA signaling has been well studied in fin regeneration of zebrafish (Blum and Begemann, 2012). Gene aldhla-2 codes for the enzyme responsible for synthesizing RA and is found to be regulated in adult zebrafish on regenerating caudal fins 24 hours after amputation (hpa) (Mathew et al, 2009 ).…”

“…Blastema formation is impeded when RA signaling pathways are suppressed. Retinoic acid molecular signaling pathways govern the blastema formation at the early stages where fin ray mesenchymal cells get proliferated and move to amputation sites form blastema (Blum and Begemann, 2012). Mitogen activity of RA signaling pathway may have a correspondence with stem cell proliferation.…”