Abstract
Background Almost all CpG-rich promoters in the mammalian genome are bound by the multidomain FBXL10 protein (also known as KDM2B, JHDM1B, CXXC2, and NDY1). FBXL10 is expressed as two isoforms: FBXL10-1, a longer form that contains an N-terminal histone demethylase domain with C-terminal F-box, CXXC, PHD, RING, and leucine-rich repeat domains, and FBXL10-2, a shorter form that initiates at an alternative internal exon and which lacks the histone demethylase domain but retains all other annotated domains. Selective deletion of Fbxl10-1 had been reported to produce a low penetrance and variable phenotype; most of the mutant animals were essentially normal. We constructed mutant mouse strains that were either null for Fbxl10-2 but wild type for Fbxl10-1 or null for both Fbxl10-1 and Fbxl10-2.ResultsDeletion of Fbxl10-2 (in a manner that does not perturb expression of Fbxl10-1) produced a phenotype very different from the Fbxl10-1 mutant, with craniofacial abnormalities, neural tube defects, and increased lethality, especially in females. Mutants that lacked both FBXL10-1 and FBXL10-2 showed embryonic lethality and even more extreme sexual dimorphism, with more severe gene dysregulation in mutant female embryos. X-linked genes were most severely dysregulated, and there was marked overexpression of Xist in mutant females although genes that encode factors that bind to Xist RNA were globally downregulated in mutant female as compared to male embryos.ConclusionsFBXL10 is the first factor shown to be required both for the normal expression and function of the Xist gene and for normal expression of proteins that associate with Xist RNA; it is proposed that FBXL10 coordinates the expression of Xist RNA with proteins that associate with this RNA. The function of FBXL10 is largely independent of the histone demethylase activity of the long form of the protein.Electronic supplementary materialThe online version of this article (doi:10.1186/s13072-016-0069-1) contains supplementary material, which is available to authorized users.
Highlights
Almost all CpG-rich promoters in the mammalian genome are bound by the multidomain FBXL10 protein
We further investigated the sexual dimorphism in embryos that lacked both FBXL10-1 and FBXL10-2 and found dysregulation of many genes in female embryos, with pronounced dysregulation of X-linked genes and strong overexpression of Xist in female embryos, with a net decrease in X-linked gene expression that was not detectable in male embryos
Selective deletion of FBXL10‐2: sexually dimorphic phenotype distinct from FBXL10‐1 mutation As shown in Fig. 1a, b, FBXL10-2 differs from FBXL10-1 by the absence of an N-terminal domain that contains a
Summary
Almost all CpG-rich promoters in the mammalian genome are bound by the multidomain FBXL10 protein ( known as KDM2B, JHDM1B, CXXC2, and NDY1). FBXL10 is a multidomain chromosomal protein that is localized to essentially all CpG-rich promoters via a CXXC domain that binds to unmethylated CpG dinucleotides [1, 3]. Ablation of the long form of the protein (the JmjCcontaining FBXL10-1) was reported to produce a fully recessive phenotype in which most homozygous mice were of normal phenotype but some displayed coloboma, exencephaly, and rare tail kinks [10]. A deletion that removed the CXXC domain (which is common to both FBXL10-1 and FBXL10-2) was reported to produce increased lethality and developmental abnormalities in heterozygous mice as a result of haploinsufficiency, but this mutant allele produced large amounts of an abnormal protein that could have exerted neomorphic effects [4]. The semidominant character of this allele contrasts with the fully recessive nature of all other mutant alleles of Fbxl (including alleles described here)
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