Roles for Dnmt3b in mammalian development: a mouse model for the ICF syndrome

Abstract

ICF (Immunodeficiency, Centromeric instability and Facial anomalies) syndrome is a rare autosomal recessive disease caused by mutations in the DNA methyltransferase gene DNMT3B. To investigate the function of Dnmt3b in mouse development and to create animal models for ICF syndrome, we have generated three mutant alleles of Dnmt3b in mice: one carrying a deletion of the catalytic domain (null allele) and two carrying ICF-like missense mutations in the catalytic domain. The Dnmt3b null allele results in embryonic lethality from E14.5 to E16.5 with multiple tissue defects, including liver hypotrophy, ventricular septal defect and haemorrhage. By contrast, mice homozygous for the ICF mutations develop to term and some survive to adulthood. These mice show phenotypes that are reminiscent of ICF patients, including hypomethylation of repetitive sequences, low body weight, distinct cranial facial anomalies and T cell death by apoptosis. These results indicate that Dnmt3b plays an essential role at different stages of mouse development, and that ICF missense mutations cause partial loss of function. These mutant mice will be useful for further elucidation of the pathogenic and molecular mechanisms underlying ICF syndrome.

Dnmt3b recruitment through E2F6 transcriptional repressor mediates germ-line gene silencing in murine somatic tissues

“…The Dnmt3b hypomorphic mutant mice we generated exhibit growth defects, skull anomalies, high rate of mortality at birth, and hypomethylation of minor satellite sequences, similar to what was observed in a previously described mouse model (40). However, a deeper analysis of the skeleton revealed severe skull defects and posterior homeotic transformations that often reflect Hox genes deregulation (33).…”

Heterogeneous clinical presentation in ICF syndrome: correlation with underlying gene defects

“…Dnmt3b deficiency results in embryonic lethality in mice aged E14.5-E16.5, with multiple tissue defects including ventricular septal defect. 21 In agreement, congenital heart defects were also observed in three patients with DNMT3B mutations. Furthermore, two ICF2 patients carrying mutations in ZBTB24 had a cardiac defect, suggesting the effects of this gene on embryonic development.…”

“…Flowcytometric analysis of CD4, CD8 and TCRb expression revealed no developmental defect of the T-cells in the thymus of newborn mice. 21 Likewise, in young ICF patients, the numbers of CD3 þ T-cells, CD4 þ and CD8 þ T-cell subsets are normal, irrespective of the group. However, in vitro stimulation of PBMCs with PHA/IL-2 and irradiated allogeneic feeders revealed that the expansion of T-cells was reduced in all ICF1 and ICF2 cases investigated.…”

“…Alternatively, the reduction in T-cell numbers after stimulation could also be caused by an increased susceptibility to apoptosis of ICF1 and ICF2 T-cells, which is in line with the results obtained with splenocytes of Dnmt3b mutant mice. 21 All ICF2 patients are intellectually disabled, and nearly all have a delay in development of walking and initial speech. In contrast, only half of the patients with ICF1 are intellectually disabled.…”

Cancer cells express aberrant DNMT3B transcripts encoding truncated proteins

“…Patients with a rare autosomal recessive syndrome, the immunodeficiency, centromere instability, facial anomalies (ICF) syndrome, have germline mutations in the DNMT3B gene (Hansen et al, 1999;Xu et al, 1999;Shirohzu et al, 2002), and lymphocytes from affected individuals display hypomethylation of repetitive DNA sequences. Furthermore, mice expressing Dnmt3b alleles similar to those found in ICF syndrome are small with abnormal craniofacial development and hypomethylation of repetitive elements, suggesting that these alleles encode hypomorphic proteins (Ueda et al, 2006).…”