No evidence for cumulative effects in a Dnmt3b hypomorph across multiple generations.

Observations of inherited phenotypes that cannot be explained solely through genetic inheritance are increasing. Evidence points to transmission of non-DNA molecules in the gamete as mediators of the phenotypes. However, in most cases it is unclear what the molecules are, with DNA methylation, chromatin proteins, and small RNAs being the most prominent candidates. From a screen to generate novel mouse mutants of genes involved in epigenetic reprogramming, we produced a DNA methyltransferase 3b allele that is missing exon 13. Mice that are homozygous for the mutant allele have smaller stature and reduced viability, with particularly high levels of female post-natal death. Reduced DNA methylation was also detected at telocentric repeats and the X-linked Hprt gene. However, none of the abnormal phenotypes or DNA methylation changes worsened with multiple generations of homozygous mutant inbreeding. This suggests that in our model the abnormalities are reset each generation and the processes of transgenerational epigenetic reprogramming are effective in preventing their inheritance.

GATA1 directly mediates interactions with closely spaced pseudopalindromic but not distantly spaced double GATA sites on DNA.

The transcription factor GATA1 helps regulate the expression of thousands of genes involved in blood development, by binding to single or double GATA sites on DNA. An important part of gene activation is chromatin looping, the bringing together of DNA elements that lie up to many thousands of basepairs apart in the genome. It was recently suggested, based on studies of the closely related protein GATA3, that GATA-mediated looping may involve interactions of each of two zinc fingers (ZF) with distantly spaced DNA elements. Here we present a structure of the GATA1 ZF region bound to pseudopalindromic double GATA site DNA, which is structurally equivalent to a recently-solved GATA3-DNA complex. However, extensive analysis of GATA1-DNA binding indicates that although the N-terminal ZF (NF) can modulate GATA1-DNA binding, under physiological conditions the NF binds DNA so poorly that it cannot play a direct role in DNA-looping. Rather, the ability of the NF to stabilize transcriptional complexes through protein-protein interactions, and thereby recruit looping factors such as Ldb1, provides a more compelling model for GATA-mediated looping.