title: Genetic variation in MKL2 and decreased downstream PCTAIRE1 expression in extreme, fatal primary human microcephaly.
abstract: The genetic mechanisms driving normal brain development remain largely unknown. We performed genomic and immunohistochemical characterization of a novel, fatal human phenotype including extreme microcephaly with cerebral growth arrest at 14-18 weeks gestation in three full sisters born to healthy, non-consanguineous parents. Analysis of index cases and parents included familial exome sequencing, karyotyping, and genome-wide single nucleotide polymorphism (SNP) array. From proband, control and unrelated microcephalic fetal cortical tissue, we compared gene expression of RNA and targeted immunohistochemistry. Each daughter was homozygous for a rare, non-synonymous, deleterious variant in the MKL2 gene and heterozygous for a private 185 kb deletion on the paternal allele, upstream and in cis with his MKL2 variant allele, eliminating 24 CArG transcription factor binding sites and MIR4718. MKL1 was underexpressed in probands. Dysfunction of MKL2 and its transcriptional coactivation partner, serum response factor (SRF), was supported by a decrease in gene and protein expression of PCTAIRE1, a downstream target of MKL2:SRF heterodimer transcriptional activation, previously shown to result in severe microcephaly in murine models. While disruption of the MKL2:SRF axis has been associated with severe microcephaly and disordered brain development in multiple model systems, the role of this transcription factor complex has not been previously demonstrated in human brain development.
authors.affiliation: Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St. Louis, MO, USA; Department of Pediatrics.
authors.forename: E I
authors.initials: EI
authors.lastname: Ramos
authors.forename: G A
authors.initials: GA
authors.lastname: Bien-Willner
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: A E O
authors.initials: AE
authors.lastname: Hughes
authors.forename: J
authors.initials: J
authors.lastname: Giacalone
authors.forename: S
authors.initials: S
authors.lastname: Chasnoff
authors.forename: S
authors.initials: S
authors.lastname: Kulkarni
authors.forename: M
authors.initials: M
authors.lastname: Parmacek
authors.forename: F S
authors.initials: FS
authors.lastname: Cole
authors.forename: T E
authors.initials: TE
authors.lastname: Druley
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002467:Cell Nucleus / Q000235:genetics; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis* / Q000235:genetics; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008831:Microcephaly / Q000235:genetics* / Q000473:pathology; D020641:Polymorphism, Single Nucleotide; D026362:Serum Response Factor / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation / Q000235:genetics
chemical_list: C478036:MRTFB protein, human; D026362:Serum Response Factor; D014157:Transcription Factors; D018844:Cyclin-Dependent Kinases; C089463:PCTAIRE-1 protein kinase
keywords: CArG-box binding factor; MKL2; SRF; exome; microcephaly