A Non-Rogue Mutant Line Induced by ENU Mutagenesis in Paramutated Rogue Peas (Pisum sativum L.) Is Still Sensitive to the Rogue Paramutation

The spontaneously emerging rogue phenotype in peas (Pisum sativum L.), characterized by narrow and pointed leaf stipula and leaflets, was the first identified case of the epigenetic phenomenon paramutation. The crosses of homozygous or heterozygous (e.g., F1) rogue plants with non-rogue (wild type) plants, produce exclusively rogue plants in the first and all subsequent generations. The fact that the wild phenotype disappears forever, is in clear contradiction with the Mendelian rules of inheritance, a situation that impedes the positional cloning of genes involved in this epigenetic phenomenon. One way of overcoming this obstacle is the identification of plant genotypes harboring naturally occurring or artificially induced neutral alleles, non-sensitive to paramutation. So far, such alleles have never been described for the pea rogue paramutation. Here, we report the induction via 1-ethyl-1-nitrosourea (ENU) mutagenesis of a non-rogue revertant mutant in the rogue cv. Progreta, and the completely unusual fixation of the induced non-rogue phenotype through several generations. The reversion of the methylation status of two previously identified differentially methylated genomic sequences in the induced non-rogue mutant, confirms that the rogue paramutation is accompanied by alterations in DNA methylation. Nevertheless, unexpectedly, the induced non-rogue mutant showed to be still sensitive to paramutation.

An N-ethyl-N-Nitrosourea Mutagenesis Screen in Mice Reveals a Mutation in Nuclear Respiratory Factor 1 (Nrf1) Altering the DNA Methylation State and Correct Embryonic Development

We have established a genome-wide N-ethyl-N-nitrosourea (ENU) mutagenesis screen to identify novel genes playing a role in epigenetic regulation in mammals. We hypothesize that the ENU mutagenesis screen will lead to the discovery of unknown genes responsible of the maintenance of the epigenetic state as the genes found are modifiers of variegation of the transgene green fluorescent protein (GFP) expression in erythrocytes, which are named MommeD. Here we report the generation of a novel mutant mouse line, MommeD46, that carries a new missense mutation producing an amino acid transversion (L71P) in the dimerization domain of Nuclear Respiratory Factor 1 (Nrf1). The molecular characterization of the mutation reveals a decrease in the Nrf1 mRNA levels and a novel role of Nrf1 in the maintenance of the DNA hypomethylation in vivo. The heritability of the mutation is consistent with paternal imprinting and haploinsufficiency. Homozygous mutants display embryonic lethality at 14.5 days post-coitum and developmental delay. This work adds a new epi-regulatory role to Nrf1 and uncovers unknown phenotypical defects of the Nrf1 hypomorph. The generated mouse line represents a valuable resource for studying NRF1-related diseases.

Characterization of Tfrc-mutant mice with microcytic phenotypes

Key Points Novel Tfrc-mutant mouse identified in ENU mutagenesis screen with stable receptor expression. Flow imaging cytometry demonstrates microcytosis in mutants derives from dysfunctional receptor-mediated endocytosis of Tf-TfR complex.