Abstract
ABSTRACTLike other urodela amphibians, axolotls are able to regenerate lost appendages, even as adults, rendering them unique among higher vertebrates. In reaction to the severe trauma of a lost limb, apoptosis seems to be primarily implicated in the removal of injured cells and tissue homeostasis. Little, however, is known about apoptotic pathways and control mechanisms. Therefore, here we provide additional information regarding the mechanisms of tissue degradation. Expression patterns of Bcl-2 family members were analyzed using reverse transcriptase-PCR, western blotting and immunofluorescence. In our study, we identified ten putative axolotl orthologs of the Bcl-2 family. We demonstrated that BH3-only proteins are differentially expressed in some axolotl organs, while they are expressed broadly in tail composite tissue and limb regeneration blastema. The importance of Bcl-2 family members is also indicated by detecting the expression of proapoptotic protein Bak in spatial congruence to apoptosis in the early stages of limb regeneration, while Bcl-2 expression was slightly modified. In conclusion, we demonstrate that Bcl-2 family members are conserved in the axolotl and might be involved in the tissue degradation processes that occur during limb regeneration.
Highlights
Unlike humans, urodela amphibians are able to regenerate appendages and organs like their limbs, tail, spinal cord, lenses and parts of their heart and brain
We have shown that B-cell lymphoma (Bcl)-2 and Bid are co-expressed in Bcl-2 positive cells in mid-limb bud blastema and apical epithelial cap (AEC) (Fig. 8)
We investigated the expression pattern of BH3-only proteins in different axolotl tissues showing that broad expression can be found in foot, brain, heart and liver composite tissue and in dedifferentiated tissues like limb blastema
Summary
Urodela amphibians are able to regenerate appendages and organs like their limbs, tail, spinal cord, lenses and parts of their heart and brain. Missing body parts are replaced in a process called epimorphic regeneration, when terminal differentiated cells re-enter the cell cycle and proliferate. The first steps towards limb regeneration are characterized by immediate hemostasis and rapid wound closure; typically achieved by migrating epithelial cells after 24 h (Tank et al, 1976). The wound epidermis (WE) thickens to the inductive apical epithelial cap (AEC) which is indispensable for regeneration (Tank et al, 1976; Whited et al, 2011).
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