Journal Article

Dissecting the molecular mechanisms in craniofrontonasal syndrome: differential mRNA expression of mutant EFNB1 and the cellular mosaic

Reardon, William, Wieacker, Peter, Wieland, Ilse, Makarov, Roman, Goldenberg, Alice, Thierry, Patrick, Tinschert, Sigrid

2008

Overview

Craniofrontonasal syndrome (CFNS) is an X-linked malformation syndrome with variable phenotype that is caused by mutations in the ephrin-B1 gene ( EFNB1 ). Over 50% of EFNB1 mutations result in premature termination codons that may elicit mRNA degradation by the nonsense-mediated decay pathway. To assess the effects of various mutations at the transcript level, expression of EFNB1 mRNA was studied by RT-PCR in fibroblast cultures established from CFNS female patients. Compared to the wild-type and two missense mutation alleles, severe depletion of transcripts was observed for mutant alleles harbouring either splice site mutation c.407-2A>T at the exon 2/3 boundary or frameshift mutation c.377_384delTCAAGAAG in exon 2. In contrast, escape from mRNA decay was observed for mutation c.614_615delCT, which generates a premature termination codon close to the 3′-end of the penultimate exon 4 disobeying the ‘50–55 bp’ rule. These results suggest differential degradation of mutant EFNB1 transcripts by the nonsense-mediated mRNA decay pathway. Although the clinical phenotypes of the patients were not highly suggestive of a phenotype–genotype correlation, the two female patients were diagnosed with diaphragmatic hernia harbouring putative ephrin-B1 truncating mutations. Previously, disease manifestation in heterozygous females had been attributed mainly to cellular interference of divergent cell populations expressing wild-type or mutant EFNB1 , depending on the pattern of X-inactivation. Upon clonal expansion of patient cells with either the wild-type or mutant EFNB1 on the active X-chromosome, we were able to separate mutant and wild-type EFNB1 -expressing cells in vitro , further supporting the concept of cellular interference in CFNS.

• Publisher: Springer International Publishing,Nature Publishing,Nature Publishing Group
• Subject: Adult / Amino Acid Sequence / Base Sequence / Bioinformatics / Biological and medical sciences / Biomedical and Life Sciences / Biomedicine / Cells, Cultured / Child / Codon, Nonsense - genetics / Craniofacial Abnormalities - genetics / Craniofacial Abnormalities - pathology / Cytogenetics / Ephrin-B1 - biosynthesis / Ephrin-B1 - genetics / Female / Frameshift Mutation - physiology / Fundamental and applied biological sciences. Psychology / Gene Expression / General aspects. Genetic counseling / Genetics of eukaryotes. Biological and molecular evolution / Heterozygote / Human Genetics / Humans / Infant / Male / Medical genetics / Medical sciences / Molecular and cellular biology / Molecular Sequence Data / Mutation, Missense - physiology / Random Allocation / RNA Splice Sites - physiology / RNA, Messenger - biosynthesis / RNA, Messenger - genetics / Syndrome