Splicing variants in MYRF cause partial loss of function in the retinal pigment epithelium

Area of Science:

• Ophthalmology
• Genetics
• Molecular Biology

Background:

• Myelin Regulatory Factor (MYRF) is crucial for retinal pigment epithelial (RPE) development.
• C-terminal MYRF variants are associated with isolated nanophthalmos, while loss-of-function variants cause syndromic diseases.

Purpose of the Study:

• To elucidate the molecular mechanism behind the discrepancy between isolated nanophthalmos and syndromic disease caused by MYRF variants.
• To investigate the role of the MYRF C-terminus in RPE development and nanophthalmos pathogenesis.

Main Methods:

• In vitro studies using ARPE-19 cells transduced with a pathogenic C-terminal MYRF variant (dG-MYRF).
• Generation and analysis of a homozygous humanized MYRF C-terminal mouse model.
• Bioinformatic analysis of integrated single-cell RNA-sequencing data from humanized and knockout mouse models.
• Identification and characterization of novel MYRF splicing variants in patients with isolated nanophthalmos.

Main Results:

• The dG-MYRF variant reduced target gene expression and steady-state levels of the MYRF cleavage product in vitro.
• The humanized MYRF C-terminal mouse model was embryonic lethal, indicating the critical role of this region.
• Shared differentially expressed genes were observed between humanized and knockout models, with reduced effect size in the hypomorphic allele.
• Two novel MYRF splicing variants were identified in isolated nanophthalmos families, one creating a nonfunctional isoform.

Conclusions:

• The pathogenic C-terminal MYRF variant (dG-MYRF) acts as a hypomorphic allele, leading to isolated nanophthalmos through a tissue-specific threshold effect.
• The MYRF C-terminus plays a unique and critical role in RPE development, and its dysfunction underlies isolated nanophthalmos.
• These findings differentiate the pathogenic mechanisms of isolated nanophthalmos versus syndromic diseases linked to MYRF.