1. Transcriptional regulation controlling heart regeneration
Adult zebrafish possess remarkable capacity to regenerate lost cardiac tissues upon injury, a trait not shared by adult mammals. Although almost all regenerative genes are highly conserved across animal species, including zebrafish and mammals, the inability of mammals to regenerate hearts remains puzzling. This discrepancy in heart regeneration may be due to differential expression of essential genes upon cardiac injury. Previously, we identified the first Tissue Regeneration Enhancer Elements (TREEs), short DNA sequences which can activate tissue regeneration programs. Successful regeneration depends on precise regulation of TREE activity: they are activated upon injury, induce regenerative gene expression, but are then tempered after completing their function. Recent studies, including studies from my lab, has discovered a variety of zebrafish TREEs, some of which can drive injury-induced reporter gene expression in mouse hearts, indicating that the mechanisms mediating injury-induced enhancer function are evolutionarily conserved. However, we have not yet fully defined the details of how DNA sequences control or dictate TREE functions. How is TREE activity encoded within the DNA sequence? Are there groups of cardiac TREEs controlled by a common regeneration-associated regulatory network, and what roles do they play? What are the binding factors for TREEs? Our lab is focusing on decoding the regulatory logic of cardiac TREEs to understand how precise regeneration-dependent expression is encoded in the DNA sequence, to identify a cluster of cardiac TREEs (regeneration-cistrome), and to determine their binding factors. Our work will provide crucial insights into the regulatory mechanisms governing cardiac regeneration enhancer function.
2. Peripheral nervous systems (PNS) and fin regeneration
Innervation is critical for regeneration of appendages, such as fins, limbs, digit tips, as denervated appendages display impaired regeneration phenotypes. Early studies demonstrated that the degree of innervation is crucial, suggesting that nerves provide neurotrophic effects. However, cellular and molecular mechanisms governing reinnervation and interaction between nerves and appendage tissues remain elusive. Our forward genetic screening isolated the striking mutant, named temca (temperature-triggered cataplexy), which exhibits two temperature-sensitive (ts) and seemingly unrelated defects: locomotion and regeneration of amputated fins at adult stages. We defined the causative gene as scn8ab, a neuronal voltage-gated sodium channel. We found that scn8ab mutation disrupts axon regrowth and pathfinding during the early phase of regeneration, resulting in hypo-innervation, misguided axon regrowth, and consequently, impaired fin regeneration. Thus, our findings uncover a critical neuronal factor for reinnervation in the injured appendage and have opened an intriguing research direction to study neural activity and nerve dependence in appendage regeneration. In this project, we are working to elucidate cellular and molecular mechanisms underlying PNS reconstruction and neural modulation of appendage regeneration.
3. Fin regeneration
Zebrafish is amenable to forward genetic screening, a powerful approach to identify novel factors affecting the phenotype. To identify novel regeneration factors, we carried out forward genetic screening and isolated 16 mutant families exhibiting fin regeneration defects in a temperature-dependent manner. We are working with these mutant families to uncover novel genes and their cellular and molecular mechanisms in fin regeneration. Some interesting candidate genes are transcription factor, splicing factor, unidentified genes, etc. This project will construct genetic models for tissue regeneration, leading to the discovery of valuable genes regulating tissue regeneration and establishment of regenerative networks.
