Limited dedifferentiation provides replacement tissue during zebrafish fin regeneration

Abstract

Unlike humans, some vertebrate animals are able to completely regenerate damaged appendages and other organs. For example, adult zebrafish will regenerate the complex structure of an amputated caudal fin to a degree that the original and replacement fins are indistinguishable. The blastema, a mass of cells that uniquely forms following appendage amputation in regenerating animals, is the major source of regenerated tissue. However, the cell lineage(s) that contribute to the blastema and their ultimate contribution(s) to the regenerated fin have not been definitively characterized. It has been suggested that cells near the amputation site dedifferentiate forming multipotent progenitors that populate the blastema and then give rise to multiple cell types of the regenerated fin. Other studies propose that blastema cells are non-uniform populations that remain restricted in their potential to contribute to different cell lineages. We tested these models by using inducible Cre-lox technology to generate adult zebrafish with distinct, isolated groups of genetically labeled cells within the caudal fin. We then tracked populations of several cell types over the entire course of fin regeneration in individual animals. We found no evidence for the existence of multipotent progenitors. Instead, multiple cell types, including epidermal cells, intra-ray fibroblasts, and osteoblasts, contribute to the newly regenerated tissue while remaining highly restricted with respect to their developmental identity. Our studies further demonstrate that the regenerating fin consists of many repeating blastema “units” dedicated to each fin ray. These blastema each have an organized structure of lineage restricted, dedifferentiated cells that cooperate to regenerate the caudal fin.

Osteoblast de- and redifferentiation is controlled by a dynamic response to retinoic acid during zebrafish fin regeneration

“…During fin regeneration osteoblasts switch from a non-cycling, matrix-producing (mature) state to a cycling, less differentiated ( preosteoblastic) state, and vice versa (supplementary material Fig. S1; Knopf et al, 2011;Sousa et al, 2011;Stewart and Stankunas, 2012). This remarkable behavior allows rapid replacement of lost bone.…”

“…Differentiation progresses in a distal-to-proximal direction, so that fast cycling preosteoblasts at the distal leading edge of aligned osteoblasts become slow-cycling differentiating cells, which subsequently mature into non-cycling matrix-producing cells (Stewart et al, 2014). Despite their dedifferentiation, osteoblasts remain lineage restricted (Knopf et al, 2011;Stewart and Stankunas, 2012). To achieve proper reconstitution of lost bone, appropriate ratios between osteoblast dedifferentiation, proliferation and redifferentiation must be tightly controlled.…”

Retinoic acid signaling spatially restricts osteoblasts and controls ray-interray organization during zebrafish fin regeneration

“…The principles that compel regenerating fin rays to respect ray-interray boundaries, therefore confining regenerating bone to extend the existing rays, are still unknown. Upon fin amputation, osteoblasts that cover the hemiray surfaces dedifferentiate into proliferating preosteoblasts and migrate into the nascent blastema, where they align at proximal lateral positions (Knopf et al, 2011;Sousa et al, 2011;Stewart and Stankunas, 2012). Thus, preosteoblasts form a layer between the basal epidermal layer and fibroblast-derived blastema cells.…”

Adenosine enhances progenitor cell recruitment and nerve growth via its A2B receptor during adult fin regeneration

“…A major issue that remains is how to control the cellular neighbourhoods in order to promote the differentiated/progenitor transition in vivo, and in this context, epimorphic regeneration in amphibians and fish provides relevant models of integrated regeneration [15,16]. Although it seems that any type of differentiated cell is able to participate in blastema formation [6,[53][54][55][56][57], only a few types will respond to injury by progressing towards progenitor identity. The lesion must induce a response that is differentially sensed by stump cells.…”