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

Abstract

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.

• Authors: Ilse Wieland, Roman Makarov, William Reardon, Sigrid Tinschert, Alice Goldenberg, Patrick Thierry, Peter Wieacker
• Journal: European journal of human genetics : EJHG (Eur J Hum Genet) Vol. 16 Issue 2 Pg. 184-91 (Feb 2008) ISSN: 1018-4813 [Print] England
• PMID: 18043713 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Codon, Nonsense
• EFNB1 protein, human
• Ephrin-B1
• RNA Splice Sites
• RNA, Messenger

Topics

• Adult
• Amino Acid Sequence
• Base Sequence
• Cells, Cultured
• Child
• Codon, Nonsense (genetics)
• Craniofacial Abnormalities (genetics, pathology)
• Ephrin-B1 (biosynthesis, genetics)
• Female
• Frameshift Mutation (physiology)
• Heterozygote
• Humans
• Infant
• Male
• Molecular Sequence Data
• Mutation, Missense (physiology)
• RNA Splice Sites (physiology)
• RNA, Messenger (biosynthesis, genetics)
• Random Allocation
• Syndrome