134 - The N-terminal Region of EFTUD2 Is Crucial for Normal Mouse Craniofacial Development

Poster Board Number: 134
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Abstract Body : Mandibulofacial dysostosis with microcephaly (MFDM) is caused by heterozygous pathogenic variants in EFTUD2 that are distributed along the length of the gene with no genotype-phenotype correlation. We previously showed that Eftud2 heterozygous mice are fertile and viable and that embryos with homozygous deletion of exon 2 of Eftud2 in fail to implant and are not recovered. Additionally, Eftud2 heterozygous mutant embryos carrying homozygous deletion of Eftud2 in the neural tube and neural crest cells have brain and craniofacial malformations and die before birth, indicating that the sequences encoded by this exon is essential for EFTUD2 function. Exon2 of Eftud2 contains the start codon and encodes for a conserved N-terminal region of the EFTUD2 protein. However, a second methionine is found in good context in Exon3 that is predicted to produce a protein with all the functional domains of EFTUD2. We postulated that this shorter protein isoform was either not made or was unstable as we found reduced EFTUD2 levels in heterozygous mutant mice. To confirm that heterozygous reduction of Eftud2 in mice does not model MFDM, we imported a mutant mouse line carrying a predicted null allele in Eftud2 due to a LacZ and Neomycin gene trap insertion in intron 8, and LoxP sequences flanking exon 9 (Eftud2 tm1a/+). We examined heterozygous mice embryos carrying the genetrap allele and show that they are phenotypically normal between E9.5 and E16.5. However, embryos carrying two alleles of the genetrap insertion in intron 8 are not recovered at mid gestation. Furthermore, embryos double heterozygous for deletion of exon 2 and 9 in their neural crest cells and neural tube are indistinguishable from Eftud2 heterozygous mutant embryos carrying homozygous deletion of Eftud2 in those same structures. Altogether, our data suggest that the N-terminal region of EFTUD2 is crucial for its proper function. Future studies aimed at identifying the role of this specific region may provide new insights into the function of EFTUD2 in the spliceosome.