The Initiation Mechanism of Regeneration in Planarian
ZHANG Wenya1,2,3, LEI Kai1,2*
Although many studies on the molecular level have shown that regeneration is regulated by a complex gene network, the upstream initiation mechanism of the gene regulatory network remains unclear. The characteristics of anatomy, genome and phylogenetic position make planarian a good animal model for regeneration studies. Studying the initiation mechanism of planarians regeneration is critical to reveal the differences in regeneration ability in nature and to find the strategies for promoting regeneration. After the injury, the immediate response of some factors is necessary to initiate the downstream gene regulatory network of regeneration followed by the regeneration. Ion channels induce the proliferation of stem cells by changing extracellular and intracellular ion concentration. The interaction between reactive oxygen species and extracellular signal-regulated kinases activates downstream signaling pathways that regulate cell proliferation and differentiation. ATP may regulate downstream regeneration by activating purinergic receptors. The large amount of mucus produced after injury and nitric oxide may act as signal factors, which can initiate the regeneration related signal cascade through the activity of immune system. The underlying connection between nerve and epidermis initiates a series of events that promote blastema formation and subsequent regeneration. Ultimately, different factors may be involved in establishing the regeneration microenvironment which coordinates subsequential regeneration events to promote regeneration in planarians. However, the exact relationship between these potential regeneration triggers and the strong regeneration ability of planarians is still unclear. The similarities and differences between the factors that activate regeneration and those induce wound healing are also largely unknown. These questions require further investigation.
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