Abstract
Purpose :
The Hippo signaling pathway is well conserved, and was reported to regulate regeneration events in various tissues. However, it remains unclear whether the Hippo pathway regulates regeneration of damaged adult zebrafish retina. We knocked down the expression of key Hippo pathway components, including kinases Lats1/2, transcriptional regulators Yap/Taz, and transcription factor Tead, to investigate their roles on Müller glia proliferation in the light-damaged retina.
Methods :
Dark-adapted albino Tg[gfap:EGFP] zebrafish were intravitreally electroporated with morpholinos to knockdown expression of the target proteins, or injected with the drug verteporfin every 12 hours, which inhibits the interaction of Yap1 and Tead. Fish were then exposed to constant light for 16, 24, or 36 hours. Damaged retinas were analyzed by qRT-PCR, immunohistochemistry and TUNEL labeling.
Results :
Our qRT-PCR data confirmed that expression of key Hippo pathway genes (yap1, lats1, tead1a) rapidly increased in response to constant light treatment and then returned to near baseline levels by 96 hours of constant light. Immunohistochemistry revealed that Yap1 protein translocates from the Müller glia cytoplasm to the nucleus after 36 hours of constant light treatment. Compared to the standard control morphant groups, the number of proliferating Müller glia decreased significantly in yap1, taz and lats1 morphant retinas (p<0.001), while the number of proliferating Müller glia increased in lats2 morphant retinas. Injecting verteporfin, which disrupts the interaction between Yap1 and Tead, led to significantly fewer Müller glia that re-entered the cell cycle (p<0.001). Additionally, the yap1 morphant possessed a significantly greater number of TUNEL-positive inner nuclear layer cells after 24 hours of constant light treatment relative to control retinas (p<0.05).
Conclusions :
The Hippo pathway is required for maximal numbers of proliferating Müller glia in response to light-induced photoreceptor cell death in the adult zebrafish retina. Later time points will be examined to determine the potential effect of the Hippo pathway on proliferation of Müller glia-derived neuronal progenitor cells and neuronal differentiation.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.