Histone Deacetylase-Mediated Müller Glia Reprogramming through Her4.1-Lin28a Axis Is Essential for Retina Regeneration in Zebrafish

Abstract

SummaryHistone deacetylases (Hdacs) play significant roles in cellular homeostasis and tissue differentiation. Hdacs are well characterized in various systems for their physiological and epigenetic relevance. However, their significance during retina regeneration remains unclear. Here we show that inhibition of Hdac1 causes a decline in regenerative ability, and injury-dependent regulation of hdacs is essential for regulating regeneration-associated genes like ascl1a, lin28a, and repressors like her4.1 at the injury site. We show selective seclusion of Hdac1 from the proliferating Müller glia-derived progenitor cells (MGPCs) and its upregulation in the neighboring cells. Hdacs negatively regulate her4.1, which also represses lin28a and essential cytokines to control MGPCs proliferation. Interestingly, Hdacs' inhibition reversibly blocks regeneration through the repression of critical cytokines and other regeneration-specific genes, which is also revealed by whole-retina RNA sequence analysis. Our study shows mechanistic understanding of the Hdac pathway during zebrafish retina regeneration.

Oct4 mediates Müller glia reprogramming and cell cycle exit during retina regeneration in zebrafish

“…Furthermore, the overexpression of Oct4 also caused a reduction in the expression of lin28a (Fig 5K) and an anticipated up-regulation in let-7a miRNA levels (Fig 5L) in 2 dpi retina. Interestingly, oct4 mRNA transfection caused an up-regulation of ascl1a mRNA (Fig S4H and I) without causing a concomitant increase in its protein levels (Fig S4J), which is probably because of elevated levels of let-7 miRNA, known to block the translation of ascl1a mRNA during retina regeneration (Ramachandran et al, 2010a; Mitra et al, 2018). These observations also support the idea that let-7a miRNA–mediated gene repression events would be crucial in contributing to the reduced MGPCs proliferation in Oct4 overexpressed retina.…”

“…The analysis of the lin28a promoter did not show any Oct4-BS, which ruled out the possibility of Oct4 directly regulating lin28a . We then explored if the lin28a could be regulated through Her4.1, an effector of Delta-Notch signaling and transcriptional repressor of lin28a in regenerating retina (Mitra et al, 2018). We saw a significant decline in her4.1 levels in oct4 knockdown retina (Fig 2G–I), which explained the up-regulated lin28a levels.…”

“…We speculated a differential affinity collaboration of Oct4 with transcriptional repressors such as histone deacetylase1 (Hdac1) during retina regeneration. Earlier studies have demonstrated the dependence of retina regeneration on differential regulation of Hdac1 in zebrafish (Mitra et al, 2018) and mice (Jorstad et al, 2017). To decipher if the differential collaboration of Oct4-Hdac1 existed, we decided to do a Co-IP of Oct4–Hdac1 complex using antibodies targeting both these proteins at various times postretinal injury.…”

Inflammation‐induced mammalian target of rapamycin signaling is essential for retina regeneration

“…Müller glia reprogramming and proliferation in zebrafish are regulated by many extrinsic cues including Heparin‐Binding Epidermal‐like Growth Factor (HB‐EGF), Wnt, Fibroblast Growth Factor (FGF), Insulin, Insulin‐like Growth Factor (IGF), Tumor Necrosis Factor alpha (TNFα), and Transforming Growth Factor beta (TGFβ), as well as cell‐intrinsic factors such as Ascl1a, Lin‐28a, Insm1a, and Pax6a/6b (Goldman, ; Lenkowski & Raymond, ). Epigenetic regulations such as DNA methylation and histone acetylation are also required for this process (Mitra et al, ; Powell, Grant, Cornblath, & Goldman, ). However, mechanisms controlling MGPC migration and differentiation remain poorly understood.…”

Epigenetic Regulation of Organ Regeneration in Zebrafish

“…In retinal regeneration, Hdac1 inhibition suppresses the formation and differentiation of MGPCs, and results in compromised regeneration. Hdac1 is an essential regulator of the genes associated with retinal regeneration, such as ascl1a , lin28a , and her4.1 [49]. Future studies need to pay more attention to profiling the global histone modifications and identifying the genes they affect during organ regeneration.…”