Yap haploinsufficiency leads to Müller cell dysfunction and late-onset cone dystrophy

Robust reprogramming of glia into neurons by inhibition of Notch signaling and nuclear factor I (NFI) factors in adult mammalian retina

Generation of neurons through direct reprogramming has emerged as a promising therapeutic approach for treating neurodegenerative diseases. In this study, we present an efficient method for reprogramming retinal glial cells into neurons. By suppressing Notch signaling by disrupting either Rbpj or Notch1/2, we induced mature Müller glial cells to reprogram into bipolar- and amacrine-like neurons. We demonstrate that Rbpj directly activates both Notch effector genes and genes specific to mature Müller glia while indirectly repressing expression of neurogenic basic helix-loop-helix (bHLH) factors. Combined loss of function of Rbpj and Nfia/b/x resulted in conversion of nearly all Müller glia to neurons. Last, inducing Müller glial proliferation by overexpression of dominant-active Yap promotes neurogenesis in both Rbpj- and Nfia/b/x/Rbpj-deficient Müller glia. These findings demonstrate that Notch signaling and NFI factors act in parallel to inhibit neurogenic competence in mammalian Müller glia and help clarify potential strategies for regenerative therapies aimed at treating retinal dystrophies.

YAP in development and disease: Navigating the regulatory landscape from retina to brain

The distinctive role of Yes-associated protein (YAP) in the nervous system has attracted widespread attention. This comprehensive review strategically uses the retina as a vantage point, embarking on an extensive exploration of YAP's multifaceted impact from the retina to the brain in development and pathology. Initially, we explore the crucial roles of YAP in embryonic and cerebral development. Our focus then shifts to retinal development, examining in detail YAP's regulatory influence on the development of retinal pigment epithelium (RPE) and retinal progenitor cells (RPCs), and its significant effects on the hierarchical structure and functionality of the retina. We also investigate the essential contributions of YAP in maintaining retinal homeostasis, highlighting its precise regulation of retinal cell proliferation and survival. In terms of retinal-related diseases, we explore the epigenetic connections and pathophysiological regulation of YAP in diabetic retinopathy (DR), glaucoma, and proliferative vitreoretinopathy (PVR). Lastly, we broaden our exploration from the retina to the brain, emphasizing the research paradigm of "retina: a window to the brain." Special focus is given to the emerging studies on YAP in brain disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), underlining its potential therapeutic value in neurodegenerative disorders and neuroinflammation.

Uveitic glaucoma-like features in Yap conditional knockout mice

Glaucoma is a multifactorial neurodegenerative disease characterized by the progressive and irreversible degeneration of the optic nerve and retinal ganglion cells. Despite medical advances aiming at slowing degeneration, around 40% of treated glaucomatous patients will undergo vision loss. It is thus of utmost importance to have a better understanding of the disease and to investigate more deeply its early causes. The transcriptional coactivator YAP, an important regulator of eye homeostasis, has recently drawn attention in the glaucoma research field. Here we show that Yap conditional knockout mice (Yap cKO), in which the deletion of Yap is induced in both Müller glia (i.e. the only retinal YAP-expressing cells) and the non-pigmented epithelial cells of the ciliary body, exhibit a breakdown of the aqueous-blood barrier, accompanied by a progressive collapse of the ciliary body. A similar phenotype is observed in human samples that we obtained from patients presenting with uveitis. In addition, aged Yap cKO mice harbor glaucoma-like features, including deregulation of key homeostatic Müller-derived proteins, retinal vascular defects, optic nerve degeneration and retinal ganglion cell death. Finally, transcriptomic analysis of Yap cKO retinas pointed to early-deregulated genes involved in extracellular matrix organization potentially underlying the onset and/or progression of the observed phenotype. Together, our findings reveal the essential role of YAP in preserving the integrity of the ciliary body and retinal ganglion cells, thereby preventing the onset of uveitic glaucoma-like features.

Robust reprogramming of glia into neurons by inhibition of Notch signaling and NFI factors in adult mammalian retina

Generation of neurons through direct reprogramming has emerged as a promising therapeutic approach for neurodegenerative diseases. Despite successful applications in vitro , in vivo implementation has been hampered by low efficiency. In this study, we present a highly efficient strategy for reprogramming retinal glial cells into neurons by simultaneously inhibiting key negative regulators. By suppressing Notch signaling through the removal of its central mediator Rbpj, we induced mature Müller glial cells to reprogram into bipolar and amacrine neurons in uninjured adult mouse retinas, and observed that this effect was further enhanced by retinal injury. We found that specific loss of function of Notch1 and Notch2 receptors in Müller glia mimicked the effect of Rbpj deletion on Müller glia-derived neurogenesis. Integrated analysis of multiome (scRNA- and scATAC-seq) and CUT&Tag data revealed that Rbpj directly activates Notch effector genes and genes specific to mature Müller glia while also indirectly represses the expression of neurogenic bHLH factors. Furthermore, we found that combined loss of function of Rbpj and Nfia/b/x resulted in a robust conversion of nearly all Müller glia to neurons. Finally, we demonstrated that inducing Müller glial proliferation by AAV (adeno-associated virus)-mediated overexpression of dominant- active Yap supports efficient levels of Müller glia-derived neurogenesis in both Rbpj - and Nfia/b/x/Rbpj - deficient Müller glia. These findings demonstrate that, much like in zebrafish, Notch signaling actively represses neurogenic competence in mammalian Müller glia, and suggest that inhibition of Notch signaling and Nfia/b/x in combination with overexpression of activated Yap could serve as an effective component of regenerative therapies for degenerative retinal diseases.

The NDR/LATS protein kinases in neurobiology: Key regulators of cell proliferation, differentiation and migration in the ocular and central nervous system

Nuclear Dbf2-related (NDR) kinases are a subgroup of evolutionarily conserved AGC protein kinases that regulate various aspects of cell growth and morphogenesis. There are 4 NDR protein kinases in mammals, LATS1, LATS2 and STTK8/NDR1, STK38L/NDR2 protein kinases. LATS1 and 2 are core components of the well-studied Hippo pathway, which play a critical role in the regulation of cell proliferation, differentiation, and cell migration via YAP/TAZ transcription factor. The Hippo pathways play an important role in nervous tissue development and homeostasis, especially with regard to the central nervous system (CNS) and the ocular system. The ocular system is a very complex system generated by the interaction in a very tightly coordinated manner of numerous and diverse developing tissues, such as, but not limited to choroidal and retinal blood vessels, the retinal pigmented epithelium and the retina, a highly polarized neuronal tissue. The retina development and maintenance require precise and coordinated regulation of cell proliferation, cell death, migration, morphogenesis, synaptic connectivity, and balanced homeostasis. This review highlights the emerging roles of NDR1 and NDR2 kinases in the regulation of retinal/neuronal function and homeostasis via a noncanonical branch of the Hippo pathway. We highlight a potential role of NDR1 and NDR2 kinases in regulating neuronal inflammation and as potential therapeutic targets for the treatment of neuronal diseases.

Retina regeneration: lessons from vertebrates

Unlike mammals, vertebrates such as fishes and frogs exhibit remarkable tissue regeneration including the central nervous system. Retina being part of the central nervous system has attracted the interest of several research groups to explore its regenerative ability in different vertebrate models including mice. Fishes and frogs completely restore the size, shape and tissue structure of an injured retina. Several studies have unraveled molecular mechanisms underlying retina regeneration. In teleosts, soon after injury, the Müller glial cells of the retina reprogram to form a proliferating population of Müller glia-derived progenitor cells capable of differentiating into various neural cell types and Müller glia. In amphibians, the transdifferentiation of retinal pigment epithelium and differentiation of ciliary marginal zone cells contribute to retina regeneration. In chicks and mice, supplementation with external growth factors or genetic modifications cause a partial regenerative response in the damaged retina. The initiation of retina regeneration is achieved through sequential orchestration of gene expression through controlled modulations in the genetic and epigenetic landscape of the progenitor cells. Several developmental biology pathways are turned on during the Müller glia reprogramming, retinal pigment epithelium transdifferentiation and ciliary marginal zone differentiation. Further, several tumorigenic pathways and gene expression events also contribute to the complete regeneration cascade of events. In this review, we address the various retinal injury paradigms and subsequent gene expression events governed in different vertebrate species. Further, we compared how vertebrates such as teleost fishes and amphibians can achieve excellent regenerative responses in the retina compared with their mammalian counterparts.

Specific ablation of Hippo signalling component Yap1 in retinal progenitors and Müller cells results in late onset retinal degeneration

Yes-associated protein (YAP) is a major component of the Hippo pathway involved in development, growth, repair and homeostasis. Nonsense YAP1 mutations in humans result in autosomal dominant coloboma. Here, we generated a conditional knockout mouse model in which Yap1 was specifically deleted in embryonic retinal progenitor cells (RPCs) and in mature Müller cells using a Chx10-Cre driver. Our data demonstrated that the conditional ablation of Yap1 in embryonic RPCs does not prevent normal retinal development and caused no gross changes in retinal structure during embryonic and early postnatal life. Nevertheless, Yap1 deficient in retinal Müller cells in adult mice leads to impaired visual responses and extensive late-onset retinal degeneration, characterized by reduced cell number in all retinal layers. Immunofluorescence data further revealed the degeneration and death of rod and cone photoreceptors, bipolar cells, horizontal cells, amacrine cells and ganglion cells to varying degrees in aged knockout mice. Moreover, alteration of glial homeostasis and reactive gliosis were also observed. Finally, cell proliferation and TUNEL assay revealed that the broad retinal degeneration is mainly caused by enhanced apoptosis in late period. Together, this work uncovers that YAP is essential for the normal vision and retinal maintenance, highlighting the crucial role of YAP in retinal function and homeostasis.

De novo frameshift mutation in YAP1 associated with bilateral uveal coloboma and microphthalmia

BACKGROUND

Uveal colobomata are eye defects that result from failure of the optic fissure of the neuroectoderm-derived optic cup to close between weeks 5-7 of fetal life. Mutations in YAP1 have previously been linked to uveal coloboma. We present the clinical features and genetic basis of a one-year-old male with bilateral uveal colobomata.

MATERIALS AND METHODS

Clinical features were gathered from an age-appropriate evaluation and retrospectively from clinical records. DNA samples were collected from the proband, his uncle (who also had coloboma), both parents, and one sibling. Whole-genome sequencing of the coding regions and intron-exon boundaries confirmed a mutation in the proband. These genetic findings were verified using the Sanger method of DNA sequencing.

RESULTS

The proband is a male with congenital bilateral colobomata (iris/retina/nerve), reduced vision, nystagmus with null point, bilateral microcornea, right microphthalmia, possible mild right hemifacial microsomia, a tubular nose, possible spina bifida occulta, and astigmatism. Whole-genome sequencing confirmed a heterozygous YAP1 frameshift mutation NM_001130145.3:c.178dupG p.(Asp60GlyfsTer52) in the proband. This mutation was absent in all other tested family members.

CONCLUSIONS

We report a de novo mutation in YAP1 that likely results in nonsense-mediated decay. Given the association with YAP1 haploinsufficiency and colobomatous microphthalmia, this novel variant provides a molecular diagnosis for the proband. Further insight into YAP1 mutations may have implications in the prevention/treatment of uveal coloboma and other syndromic disorders.

The Molecular Network of YAP/Yorkie at the Cell Cortex and their Role in Ocular Morphogenesis

During development, the precise control of tissue morphogenesis requires changes in the cell number, size, shape, position, and gene expression, which are driven by both chemical and mechanical cues from the surrounding microenvironment. Such physical and architectural features inform cells about their proliferative and migratory capacity, enabling the formation and maintenance of complex tissue architecture. In polarised epithelia, the apical cell cortex, a thin actomyosin network that lies directly underneath the apical plasma membrane, functions as a platform to facilitate signal transmission between the external environment and downstream signalling pathways. One such signalling pathway culminates in the regulation of YES-associated protein (YAP) and TAZ transcriptional co-activators and their sole Drosophila homolog, Yorkie, to drive proliferation and differentiation. Recent studies have demonstrated that YAP/Yorkie exhibit a distinct function at the apical cell cortex. Here, we review recent efforts to understand the mechanisms that regulate YAP/Yki at the apical cell cortex of epithelial cells and how normal and disturbed YAP-actomyosin networks are involved in eye development and disease.