The RBPome of influenza A virus NP-mRNA reveals a role for TDP-43 in viral replication.

Genome-wide approaches have significantly advanced our knowledge of the repertoire of RNA-binding proteins (RBPs) that associate with cellular polyadenylated mRNAs within eukaryotic cells. Recent studies focusing on the RBP interactomes of viral mRNAs, notably SARS-Cov-2, have revealed both similarities and differences between the RBP profiles of viral and cellular mRNAs. However, the RBPome of influenza virus mRNAs remains unexplored. Herein, we identify RBPs that associate with the viral mRNA encoding the nucleoprotein (NP) of an influenza A virus. Focusing on TDP-43, we show that it binds several influenza mRNAs beyond the NP-mRNA, and that its depletion results in lower levels of viral mRNAs and proteins within infected cells, and a decreased yield of infectious viral particles. We provide evidence that the viral polymerase recruits TDP-43 onto viral mRNAs through a direct interaction with the disordered C-terminal domain of TDP-43. Notably, other RBPs found to be associated with influenza virus mRNAs also interact with the viral polymerase, which points to a role of the polymerase in orchestrating the assembly of viral messenger ribonucleoproteins.

Mapping of pseudouridine residues on cellular and viral transcripts using a novel antibody-based technique.

Pseudouridine (Ψ) is the most common noncanonical ribonucleoside present on mammalian noncoding RNAs (ncRNAs), including rRNAs, tRNAs, and snRNAs, where it contributes ∼7% of the total uridine level. However, Ψ constitutes only ∼0.1% of the uridines present on mRNAs and its effect on mRNA function remains unclear. Ψ residues have been shown to inhibit the detection of exogenous RNA transcripts by host innate immune factors, thus raising the possibility that viruses might have subverted the addition of Ψ residues to mRNAs by host pseudouridine synthase (PUS) enzymes as a way to inhibit antiviral responses in infected cells. Here, we describe and validate a novel antibody-based Ψ mapping technique called photo-crosslinking-assisted Ψ sequencing (PA-Ψ-seq) and use it to map Ψ residues on not only multiple cellular RNAs but also on the mRNAs and genomic RNA encoded by HIV-1. We describe 293T-derived cell lines in which human PUS enzymes previously reported to add Ψ residues to human mRNAs, specifically PUS1, PUS7, and TRUB1/PUS4, were inactivated by gene editing. Surprisingly, while this allowed us to assign several sites of Ψ addition on cellular mRNAs to each of these three PUS enzymes, Ψ sites present on HIV-1 transcripts remained unaffected. Moreover, loss of PUS1, PUS7, or TRUB1 function did not significantly reduce the level of Ψ residues detected on total human mRNA below the ∼0.1% level seen in wild-type cells, thus implying that the PUS enzyme(s) that adds the bulk of Ψ residues to human mRNAs remains to be defined.

Influenza A virus-derived siRNAs increase in the absence of NS1 yet fail to inhibit virus replication.

While the issue of whether RNA interference (RNAi) ever forms part of the antiviral innate immune response in mammalian somatic cells remains controversial, there is considerable evidence demonstrating that few, if any, viral small interfering RNAs (siRNAs) are produced in infected cells. Moreover, inhibition of RNAi by mutational inactivation of key RNAi factors, such as Dicer or Argonaute 2, fails to enhance virus replication. One potential explanation for this lack of inhibitory effect is that mammalian viruses encode viral suppressors of RNAi (VSRs) that are so effective that viral siRNAs are not produced in infected cells. Indeed, a number of mammalian VSRs have been described, of which the most prominent is the influenza A virus (IAV) NS1 protein, which has not only been reported to inhibit RNAi in plants and insects but also to prevent the production of viral siRNAs in IAV-infected human cells. Here, we confirm that an IAV mutant lacking NS1 indeed differs from wild-type IAV in that it induces the production of readily detectable levels of Dicer-dependent viral siRNAs in infected human cells. However, we also demonstrate that these siRNAs have little if any inhibitory effect on IAV gene expression. This is likely due, at least in part, to their inefficient loading into RNA-induced silencing complexes.

Addition of m6A to SV40 late mRNAs enhances viral structural gene expression and replication.

Polyomaviruses are a family of small DNA tumor viruses that includes several pathogenic human members, including Merkel cell polyomavirus, BK virus and JC virus. As is characteristic of DNA tumor viruses, gene expression in polyomaviruses is temporally regulated into an early phase, consisting of the viral regulatory proteins, and a late phase, consisting of the viral structural proteins. Previously, the late transcripts expressed by the prototypic polyomavirus simian virus 40 (SV40) were reported to contain several adenosines bearing methyl groups at the N6 position (m6A), although the precise location of these m6A residues, and their phenotypic effects, have not been investigated. Here, we first demonstrate that overexpression of the key m6A reader protein YTHDF2 induces more rapid viral replication, and larger viral plaques, in SV40 infected BSC40 cells, while mutational inactivation of the endogenous YTHDF2 gene, or the m6A methyltransferase METTL3, has the opposite effect, thus suggesting a positive role for m6A in the regulation of SV40 gene expression. To directly test this hypothesis, we mapped sites of m6A addition on SV40 transcripts and identified two m6A sites on the viral early transcripts and eleven m6A sites on the late mRNAs. Using synonymous mutations, we inactivated the majority of the m6A sites on the SV40 late mRNAs and observed that the resultant viral mutant replicated more slowly than wild type SV40. Alternative splicing of SV40 late mRNAs was unaffected by the reduction in m6A residues and our data instead suggest that m6A enhances the translation of viral late transcripts. Together, these data argue that the addition of m6A residues to the late transcripts encoded by SV40 plays an important role in enhancing viral gene expression and, hence, replication.

A novel role for CRIM1 in the corneal response to UV and pterygium development.

Pterygium is a pathological proliferative condition of the ocular surface, characterised by formation of a highly vascularised, fibrous tissue arising from the limbus that invades the central cornea leading to visual disturbance and, if untreated, blindness. Whilst chronic ultraviolet (UV) light exposure plays a major role in its pathogenesis, higher susceptibility to pterygium is observed in some families, suggesting a genetic component. In this study, a Northern Irish family affected by pterygium but reporting little direct exposure to UV was identified carrying a missense variant in CRIM1 NM_016441.2: c.1235 A > C (H412P) through whole-exome sequencing and subsequent analysis. CRIM1 is expressed in the developing eye, adult cornea and conjunctiva, having a role in cell differentiation and migration but also in angiogenesis, all processes involved in pterygium formation. We demonstrate elevated CRIM1 expression in pterygium tissue from additional individual Northern Irish patients compared to unaffected conjunctival controls. UV irradiation of HCE-S cells resulted in an increase in ERK phosphorylation and CRIM1 expression, the latter further elevated by the addition of the MEK1/2 inhibitor, U0126. Conversely, siRNA knockdown of CRIM1 led to decreased UV-induced ERK phosphorylation and increased BCL2 expression. Transient expression of the mutant H412P CRIM1 in corneal epithelial HCE-S cells showed that, unlike wild-type CRIM1, it was unable to reduce the cell proliferation, increased ERK phosphorylation and apoptosis induced through a decrease of BCL2 expression levels. We propose here a series of intracellular events where CRIM1 regulation of the ERK pathway prevents UV-induced cell proliferation and may play an important role in the in the pathogenesis of pterygium.

Keratin 12 missense mutation induces the unfolded protein response and apoptosis in Meesmann epithelial corneal dystrophy.

Meesmann epithelial corneal dystrophy (MECD) is a rare autosomal dominant disorder caused by dominant-negative mutations within the KRT3 or KRT12 genes, which encode the cytoskeletal protein keratins K3 and K12, respectively. To investigate the pathomechanism of this disease, we generated and phenotypically characterized a novel knock-in humanized mouse model carrying the severe, MECD-associated, K12-Leu132Pro mutation. Although no overt changes in corneal opacity were detected by slit-lamp examination, the corneas of homozygous mutant mice exhibited histological and ultrastructural epithelial cell fragility phenotypes. An altered keratin expression profile was observed in the cornea of mutant mice, confirmed by western blot, RNA-seq and quantitative real-time polymerase chain reaction. Mass spectrometry (MS) and immunohistochemistry demonstrated a similarly altered keratin profile in corneal tissue from a K12-Leu132Pro MECD patient. The K12-Leu132Pro mutation results in cytoplasmic keratin aggregates. RNA-seq analysis revealed increased chaperone gene expression, and apoptotic unfolded protein response (UPR) markers, CHOP and Caspase 12, were also increased in the MECD mice. Corneal epithelial cell apoptosis was increased 17-fold in the mutant cornea, compared with the wild-type (P < 0.001). This elevation of UPR marker expression was also observed in the human MECD cornea. This is the first reporting of a mouse model for MECD that recapitulates the human disease and is a valuable resource in understanding the pathomechanism of the disease. Although the most severe phenotype is observed in the homozygous mice, this model will still provide a test-bed for therapies not only for corneal dystrophies but also for other keratinopathies caused by similar mutations.

Viral Epitranscriptomics.

Although it has been known for over 40 years that eukaryotic mRNAs bear internal base modifications, it is only in the last 5 years that the importance of these modifications has begun to come into focus. The most common mRNA modification, the addition of a methyl group to the N6 position of adenosine (m6A), has been shown to affect splicing, translation, and stability, and m6A is also essential for embryonic development in organisms ranging from plants to mice. While all viral transcripts examined so far have been found to be extensively m6A modified, the role, if any, of m6A in regulating viral gene expression and replication was previously unknown. However, recent data generated using HIV-1 as a model system strongly suggest that sites of m6A addition not only are evolutionarily conserved but also enhance virus replication. It is therefore likely that the field of viral epitranscriptomics, which can be defined as the study of functionally relevant posttranscriptional modifications of viral RNA transcripts that do not change the nucleotide sequence of that RNA, is poised for a major expansion in scientific interest and may well fundamentally change our understanding of how viral replication is regulated.

Identifying Individual Pseudouridine (Ψ) Sites Across Transcripts from HIV-1 Infected Cells.

The identification of RNA modifications at single nucleotide resolution has become an emerging area of interest within biology and specifically among virologists seeking to ascertain how this untapped area of RNA regulation may be altered or hijacked upon viral infection. Herein, we describe a straightforward biochemical approach modified from two original published Ψ mapping protocols, BID-seq and PRAISE, to specifically identify pseudouridine modifications on mRNA transcripts from an HIV-1 infected T cell line. This protocol could readily be adapted for other viral infected cell types and additionally for populations of purified virions from infected cells.

Comparison of SARS-CoV-2 Evolution in Paediatric Primary Airway Epithelial Cell Cultures Compared with Vero-Derived Cell Lines.

SARS-CoV-2 can efficiently infect both children and adults, albeit with morbidity and mortality positively associated with increasing host age and presence of co-morbidities. SARS-CoV-2 continues to adapt to the human population, resulting in several variants of concern (VOC) with novel properties, such as Alpha and Delta. However, factors driving SARS-CoV-2 fitness and evolution in paediatric cohorts remain poorly explored. Here, we provide evidence that both viral and host factors co-operate to shape SARS-CoV-2 genotypic and phenotypic change in primary airway cell cultures derived from children. Through viral whole-genome sequencing, we explored changes in genetic diversity over time of two pre-VOC clinical isolates of SARS-CoV-2 during passage in paediatric well-differentiated primary nasal epithelial cell (WD-PNEC) cultures and in parallel, in unmodified Vero-derived cell lines. We identified a consistent, rich genetic diversity arising in vitro, variants of which could rapidly rise to near fixation within two passages. Within isolates, SARS-CoV-2 evolution was dependent on host cells, with paediatric WD-PNECs showing a reduced diversity compared to Vero (E6) cells. However, mutations were not shared between strains. Furthermore, comparison of both Vero-grown isolates on WD-PNECs disclosed marked growth attenuation mapping to the loss of the polybasic cleavage site (PBCS) in Spike, while the strain with mutations in Nsp12 (T293I), Spike (P812R) and a truncation of Orf7a remained viable in WD-PNECs. Altogether, our work demonstrates that pre-VOC SARS-CoV-2 efficiently infects paediatric respiratory epithelial cells, and its evolution is restrained compared to Vero (E6) cells, similar to the case of adult cells. We highlight the significant genetic plasticity of SARS-CoV-2 while uncovering an influential role for collaboration between viral and host cell factors in shaping viral evolution and ultimately fitness in human respiratory epithelium.

Post-Transcriptional Regulation of Viral RNA through Epitranscriptional Modification.

The field of mRNA modifications has been steadily growing in recent years as technologies have improved and the importance of these residues became clear. However, a subfield has also arisen, specifically focused on how these modifications affect viral RNA, with the possibility that viruses can also be used as a model to best determine the role that these modifications play on cellular mRNAs. First, virologists focused on the most abundant internal mRNA modification, m6A, mapping this modification and elucidating its effects on the RNA of a wide range of RNA and DNA viruses. Next, less common RNA modifications including m5C, Nm and ac4C were investigated and also found to be present on viral RNA. It now appears that viral RNA is littered with a multitude of RNA modifications. In biological systems that are under constant evolutionary pressure to out compete both the host as well as newly arising viral mutants, it poses an interesting question about what evolutionary benefit these modifications provide as it seems evident, at least to this author, that these modifications have been selected for. In this review, I discuss how RNA modifications are identified on viral RNA and the roles that have now been uncovered for these modifications in regard to viral replication. Finally, I propose some interesting avenues of research that may shed further light on the exact role that these modifications play in viral replication.

Extensive Epitranscriptomic Methylation of A and C Residues on Murine Leukemia Virus Transcripts Enhances Viral Gene Expression.

While it has been known for several years that viral RNAs are subject to the addition of several distinct covalent modifications to individual nucleotides, collectively referred to as epitranscriptomic modifications, the effect of these editing events on viral gene expression has been controversial. Here, we report the purification of murine leukemia virus (MLV) genomic RNA to homogeneity and show that this viral RNA contains levels of N6-methyladenosine (m6A), 5-methylcytosine (m5C), and 2'O-methylated (Nm) ribonucleotides that are an order of magnitude higher than detected on bulk cellular mRNAs. Mapping of m6A and m5C residues on MLV transcripts identified multiple discrete editing sites and allowed the construction of MLV variants bearing silent mutations that removed a subset of these sites. Analysis of the replication potential of these mutants revealed a modest but significant attenuation in viral replication in 3T3 cells in culture. Consistent with a positive role for m6A and m5C in viral replication, we also demonstrate that overexpression of the key m6A reader protein YTHDF2 enhances MLV replication, while downregulation of the m5C writer NSUN2 inhibits MLV replication.IMPORTANCE The data presented in the present study demonstrate that MLV RNAs bear an exceptionally high level of the epitranscriptomic modifications m6A, m5C, and Nm, suggesting that these each facilitate some aspect of the viral replication cycle. Consistent with this hypothesis, we demonstrate that mutational removal of a subset of these m6A or m5C modifications from MLV transcripts inhibits MLV replication in cis, and a similar result was also observed upon manipulation of the level of expression of key cellular epitranscriptomic cofactors in trans Together, these results argue that the addition of several different epitranscriptomic modifications to viral transcripts stimulates viral gene expression and suggest that MLV has therefore evolved to maximize the level of these modifications that are added to viral RNAs.

Epitranscriptomic Addition of m5C to HIV-1 Transcripts Regulates Viral Gene Expression.

How the covalent modification of mRNA ribonucleotides, termed epitranscriptomic modifications, alters mRNA function remains unclear. One issue has been the difficulty of quantifying these modifications. Using purified HIV-1 genomic RNA, we show that this RNA bears more epitranscriptomic modifications than the average cellular mRNA, with 5-methylcytosine (m5C) and 2'O-methyl modifications being particularly prevalent. The methyltransferase NSUN2 serves as the primary writer for m5C on HIV-1 RNAs. NSUN2 inactivation inhibits not only m5C addition to HIV-1 transcripts but also viral replication. This inhibition results from reduced HIV-1 protein, but not mRNA, expression, which in turn correlates with reduced ribosome binding to viral mRNAs. In addition, loss of m5C dysregulates the alternative splicing of viral RNAs. These data identify m5C as a post-transcriptional regulator of both splicing and function of HIV-1 mRNA, thereby affecting directly viral gene expression.

Epitranscriptomic Enhancement of Influenza A Virus Gene Expression and Replication.

Many viral RNAs are modified by methylation of the N6 position of adenosine (m6A). m6A is thought to regulate RNA splicing, stability, translation, and secondary structure. Influenza A virus (IAV) expresses m6A-modified RNAs, but the effects of m6A on this segmented RNA virus remain unclear. We demonstrate that global inhibition of m6A addition inhibits IAV gene expression and replication. In contrast, overexpression of the cellular m6A "reader" protein YTHDF2 increases IAV gene expression and replication. To address whether m6A residues modulate IAV RNA function in cis, we mapped m6A residues on the IAV plus (mRNA) and minus (vRNA) strands and used synonymous mutations to ablate m6A on both strands of the hemagglutinin (HA) segment. These mutations inhibited HA mRNA and protein expression while leaving other IAV mRNAs and proteins unaffected, and they also resulted in reduced IAV pathogenicity in mice. Thus, m6A residues in IAV transcripts enhance viral gene expression.

Towards personalised allele-specific CRISPR gene editing to treat autosomal dominant disorders.

CRISPR/Cas9 holds immense potential to treat a range of genetic disorders. Allele-specific gene disruption induced by non-homologous end-joining (NHEJ) DNA repair offers a potential treatment option for autosomal dominant disease. Here, we successfully delivered a plasmid encoding S. pyogenes Cas9 and sgRNA to the corneal epithelium by intrastromal injection and acheived long-term knockdown of a corneal epithelial reporter gene, demonstrating gene disruption via NHEJ in vivo. In addition, we used TGFBI corneal dystrophies as a model of autosomal dominant disease to assess the use of CRISPR/Cas9 in two allele-specific systems, comparing cleavage using a SNP-derived PAM to a guide specific approach. In vitro, cleavage via a SNP-derived PAM was found to confer stringent allele-specific cleavage, while a guide-specific approach lacked the ability to distinguish between the wild-type and mutant alleles. The failings of the guide-specific approach highlights the necessity for meticulous guide design and assessment, as various degrees of allele-specificity are achieved depending on the guide sequence employed. A major concern for the use of CRISPR/Cas9 is its tendency to cleave DNA non-specifically at "off-target" sites. Confirmation that S. pyogenes Cas9 lacks the specificity to discriminate between alleles differing by a single base-pair regardless of the position in the guide is demonstrated.

Protein Composition of TGFBI-R124C- and TGFBI-R555W-Associated Aggregates Suggests Multiple Mechanisms Leading to Lattice and Granular Corneal Dystrophy.

PURPOSE: Transforming growth factor beta-induced (TGFBI)-related dystrophies constitute the most common heritable forms of corneal dystrophy worldwide. However, other than the underlying genotypes of these conditions, a limited knowledge exists of the exact pathomechanisms of these disorders. This study expands on our previous research investigating dystrophic stromal aggregates, with the aim of better elucidating the pathomechanism of two conditions arising from the most common TGFBI mutations: granular corneal dystrophy type 1 (GCD1; R555W) and lattice corneal dystrophy type 1 (LCD1; R124C). METHODS: Patient corneas with GCD1 and LCD1 were stained with hematoxylin and eosin and Congo red to visualize stromal nonamyloid and amyloid deposits, respectively. Laser capture microdissection was used to isolate aggregates and extracted protein was analyzed by mass spectrometry. Proteins were identified and their approximate abundances were determined. Spectra of TGFBIp peptides were also recorded and quantified. RESULTS: In total, three proteins were found within GCD1 aggregates that were absent in the healthy control corneal tissue. In comparison, an additional 18 and 24 proteins within stromal LCD1 and Bowman's LCD1 deposits, respectively, were identified. Variances surrounding the endogenous cleavage sites of TGFBIp were also noted. An increase in the number of residues experiencing cleavage was observed in both GCD1 aggregates and LCD1 deposits. CONCLUSIONS: The study reveals previously unknown differences between the protein composition of GCD1 and LCD1 aggregates, and confirms the presence of the HtrA1 protease in LCD1-amyloid aggregates. In addition, we find mutation-specific differences in the processing of mutant TGFBIp species, which may contribute to the variable phenotypes noted in TGFBI-related dystrophies.

Protection of corneal epithelial stem cells prevents ultraviolet A damage during corneal collagen cross-linking treatment for keratoconus.

BACKGROUND/AIMS: Cross-linking of the cornea is usually carried out at a young age as a treatment to manage ectasia. The corneal limbal region contains delicate long-lived stem cells, which could potentially be deleteriously affected by Ultraviolet A (UV-A) radiation. Damage to these stem cells may not demonstrate as a clinical problem for many years subsequent to cross-linking treatment. UV-A radiation is known to have potential mutagenic effects upon mammalian DNA and can result in cancer. METHODS: Cultured corneal epithelial cells and ex vivo corneal tissue were treated with the standard clinical cross-linking protocol for UV-A irradiation. 8-hydroxydeoxyguansoine (8-OHdG) and cyclin-dependent kinase inhibitor genes (CDKN1A and CDKN2A) were assayed as markers of DNA damage using immunohistochemistry, ELISA and quantitative real time PCR. RESULTS: Staining of treated limbal tissue demonstrated the presence of 8-OHdG within p63 positive basal limbal cells. Levels of 8-OHdG and CDKN1A mRNA were found to be significantly increased in cultured corneal epithelial cells and limbal epithelial cells but no increase was demonstrated with the use of a polymethyl methylacrylate protective cover. CONCLUSIONS: This study provides evidence that oxidative nuclear DNA damage can occur through cross-linking in layers of corneal epithelial cells at the limbus and that this can be easily prevented by covering the limbus.

siRNA silencing of the mutant keratin 12 allele in corneal limbal epithelial cells grown from patients with Meesmann's epithelial corneal dystrophy.

PURPOSE: The aim of this study is to further assess our previously reported keratin 12 (K12)-Leu132Pro specific siRNA in silencing the mutant allele in Meesmann's Epithelial Corneal Dystrophy (MECD) in experimental systems more akin to the in vivo situation through simultaneous expression of both wild-type and mutant alleles. METHODS: Using KRT12 exogenous expression constructs transfected into cells, mutant allele specific knockdown was quantified using pyrosequencing and infrared Western blot analysis, while the silencing mechanism was assessed by a modified rapid amplification of cDNA ends (5'RACE) method. Corneal limbal biopsies taken from patients suffering from MECD were used to establish cultures of MECD corneal limbal epithelial stem cells and the ability of the siRNA to silence the endogenous mutant KRT12 allele was assessed by a combination of pyrosequencing, qPCR, ELISA, and quantitative-fluorescent immunohistochemistry (Q-FIHC). RESULTS: The siRNA displayed a potent and specific knockdown of K12-Leu132Pro at both the mRNA and protein levels with exogenous expression constructs. Analysis by the 5'RACE method confirmed siRNA-mediated cleavage. In the MECD cells, an allele-specific knockdown of 63% of the endogenous mutant allele was observed without effect on wild-type allele expression. CONCLUSIONS: Combined with an effective delivery vehicle this siRNA approach represents a viable treatment option for prevention of the MECD pathology observed in K12-Leu132Pro heterozygous individuals.

Development of allele-specific gene-silencing siRNAs for TGFBI Arg124Cys in lattice corneal dystrophy type I.

PURPOSE: This study aimed to investigate the potency and specificity of short-interfering RNA (siRNA) treatment for TGFBI-Arg124Cys lattice corneal dystrophy type I (LCDI) using exogenous expression constructs in model systems and endogenous gene targeting in an ex vivo model using corneal epithelial cell cultures. METHODS: A panel of 19 TGFBI-Arg124Cys-specific siRNAs were assessed by a dual-luciferase reporter assay. Further assessment using pyrosequencing and qPCR was used to identify the lead siRNA; suppression of mutant TGFBIp expression was confirmed by Western blot and Congo red aggregation assays. An ex vivo model of LCDI was established using limbal biopsies from corneal dystrophy patients harboring the Arg124Cys mutation. Treatment efficiency of the siRNA was assessed for the inhibition of the mutant allele in the primary patient's corneal epithelial cells using pyrosequencing, quantitative PCR (qPCR), and an ELISA. RESULTS: A lead siRNA was identified, and demonstrated to be potent and specific in inhibiting the TGFBI-Arg124Cys mutant allele at the mRNA and protein levels. Besides high allele specificity, siRNA treatment achieved a 44% reduction of the endogenous Arg124Cys allele in an ex vivo model of LCDI. CONCLUSIONS: We have identified a lead siRNA specific to the TGFBI-Arg124Cys mutant allele associated with LCDI. Silencing of exogenous TGFBI was observed at mRNA and protein levels, and in an ex vivo model of LCDI with an efficient suppression of the endogenous mutant allele. This result indicates the potential of siRNA treatment as a personalized medicine approach for the management of heritable TGFBI-associated corneal dystrophies.