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Functional mechanisms of MYRF DNA-binding domain mutations implicated in birth defects.

ABSTRACT: Myrf is a pleiotropic membrane-bound transcription factor that plays critical roles in diverse organisms, including in oligodendrocyte differentiation, embryonic development, molting, and synaptic plasticity. Upon autolytic cleavage, the Myrf N-terminal fragment enters the nucleus as a homo-trimer and functions as a transcription factor. Homo-trimerization is essential for this function because it imparts DNA-binding specificity and affinity. Recent exome sequencing studies have implicated four de novo MYRF DNA-binding domain (DBD) mutations (F387S, Q403H, G435R, and L479V) in novel syndromic birth defects involving the diaphragm, heart, and the urogenital tract. It remains unknown whether and how these four mutations alter the transcription factor function of MYRF. Here, we studied them by introducing homologous mutations to the mouse Myrf protein. We found that the four DBD mutations abolish the transcriptional activity of the Myrf N-terminal fragment by interfering with its homo-trimerization ability by perturbing the DBD structure. Since the Myrf N-terminal fragment strictly functions as a homo-trimer, any loss-of-function mutation has the potential to act as a dominant negative. We observed that one copy of Myrf-F387S, Myrf-Q403H, or Myrf-L479V, but not Myrf-G435R, was tolerated by the Myrf N-terminal homo-trimer for structural and functional integrity. These data suggest that F387S, Q403H, and L479V cause birth defects by haploinsufficiency, while G435R does so via dominant negative functionality.

SUBMITTER: Fan C

PROVIDER: S-EPMC8094900 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an autosomal dominant small-vessel disease of the brain caused by mutations in the NOTCH3 receptor. The highly stereotyped nature of the mutations, which alter the number of cysteine residues within the epidermal growth factor-like repeats (EGFR), predicts that all mutations share common mechanisms. Prior in vitro assays and genetic studies in the mouse support the hypothesis that common mutations do not compromise canonical Notch3 function but instead convey a non-physiological and deleterious activity to the receptor through the unpaired cysteine residue. Intriguingly, in vitro studies predict that mutations located in the Delta/Serrate/LAG-2 ligand binding domain-(EGFR10-11) may result in a loss of Notch3 receptor function. However, the in vivo relevance and functional significance of this with respect to the pathogenic mechanisms and clinical expression of the disease remain largely unexplored. To ascertain, in vivo, the functional significance of EGFR10-11 mutations, we generated transgenic mice with one representative mutation (C428S) in EGFR10 of Notch3. These mice, like those with a common R90C mutation, developed characteristic arterial accumulation of Notch3 protein and granular osmiophilic material upon aging. By introducing the mutant C428S transgene into a Notch3 null background, we found that, unlike the R90C mutant protein, the C428S mutant protein has lost wild-type Notch3 activity and exhibited mild dominant-negative activity in three different biological settings. From a large prospectively recruited cohort of 176 CADASIL patients, we identified 10 patients, from five distinct pedigrees carrying a mutation in EGFR10 or 11. These mutations were associated with significantly higher Mini-Mental State Examination and Mattis Dementia Rating Scale scores (P < 0.05), when compared with common mutations. Additionally, we found a strong effect of this genotype on the burden of white matter hyperintensities (P < 0.01). Collectively, these results highlight distinctive functional and phenotypic features of EGFR10-11 mutations relative to the common CADASIL mutations. Our findings are compatible with the hypothesis that EGFR10-11 mutations cause the disease through the same gain of novel function as the common mutations, and lead us to propose that reduced Notch3 signalling acts as a modifier of the CADASIL phenotype.

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Functional mechanisms of MYRF DNA-binding domain mutations implicated in birth defects.

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