The Novel Roles of the Hippo Pathway in Regulating Retinal Regeneration in Adult Zebrafish

Zebrafish (Danio rerio) have the natural capacity to regenerate all neuronal cell types of the retina that are lost following injury through the reprogramming and proliferation of the Müller glia. The mechanism regulating the retinal regeneration is still elusive. Recently, the Hippo pathway effector Yap has been identified play roles in regulating the proliferation Müller glia in mice. Our previous data also showed the Yap1 is required for reprogramming and proliferation of the Müller glia. However, previous publications focused on the expression of the Hippo pathway effectors Yap1 and Taz, largely ignoring the other Hippo pathway genes. In this study, I dissected the functions of several core Hippo pathway genes during retinal damage and regeneration, which included the genes encoding three kinases stk3, lats1, lats2, two transcriptional co-activators yap1 and taz, four transcription factors tead1a, tead1b, tead3a, tead3b.

In this research, I first identified another two Hippo pathway components Tead1a and Tead3a are required for Müller glia reprogramming via regulating Sox2 expression. And I first identified the two kinases Lats1 and Lats2, and four Tead transcriptional factors played distinct roles in regulating the proliferation of Müller glia and neuronal progenitor cells. Interestingly, I identified the mechanism of Lats2 and Stk3 maintaining the quiescent exit of Müller glia via repressing the Notch3 inner cellular domain (N3ICD) expression. Combining with rescue experiments, the exciting results indicate the Notch3 ICD is a node at the crosstalk of the Hippo Pathway and the Notch pathway in regulating Müller glia quiescent exit. I further analyzed the single-cell data sets and identified the Hippo-Adam10-Notch-Notch3 ICD axis in regulating Müller glia proliferation. The novel results indicate in Müller glia during retinal regeneration: the Hippo pathway and the Notch Pathway can interact via a protease cleavage mechanism, but not through the ligands/receptors mechanism, which is a regular Hippo-Notch crosstalk mechanism.