We have developed a sensitized screen to identify genes involved in gene silencing, using random N-ethyl-N-nitrosourea mutagenesis on mice carrying a variegating GFP transgene. The dominant screen has produced six mutant lines, including both suppressors and enhancers of variegation. All are semidominant and five of the six are homozygous embryonic lethal. In one case, the homozygous lethality depends on sex: homozygous females die at midgestation and display abnormal DNA methylation of the X chromosome, whereas homozygous males are viable. Linkage analysis reveals that the mutations map to unique chromosomal locations. We have studied the effect of five of the mutations on expression of an endogenous allele known to be sensitive to epigenetic state, agouti viable yellow. In all cases, there is an effect on penetrance, and in most cases, parent of origin and sex-specific effects are detected. This screen has identified genes that are involved in epigenetic reprogramming of the genome, and the behavior of the mutant lines suggests a common mechanism between X inactivation and transgene and retrotransposon silencing. Our findings raise the possibility that the presence or absence of the X chromosome in mammals affects the establishment of the epigenetic state at autosomal loci by acting as a sink for proteins involved in gene silencing. The study demonstrates the power of sensitized screens in the mouse not only for the discovery of novel genes involved in a particular process but also for the elucidation of the biology of that process.

There is increasing evidence in both plants and animals that epigenetic marks are not always cleared between generations. Incomplete erasure at genes associated with a measurable phenotype results in unusual patterns of inheritance from one generation to the next, termed transgenerational epigenetic inheritance. The Agouti viable yellow (Avy) allele is the best-studied example of this phenomenon in mice. The Avy allele is the result of a retrotransposon insertion upstream of the Agouti gene. Expression at this locus is controlled by the long terminal repeat (LTR) of the retrotransposon, and expression results in a yellow coat and correlates with hypomethylation of the LTR. Isogenic mice display variable expressivity, resulting in mice with a range of coat colours, from yellow through to agouti. Agouti mice have a methylated LTR. The locus displays epigenetic inheritance following maternal but not paternal transmission; yellow mothers produce more yellow offspring than agouti mothers. We have analysed the DNA methylation in mature gametes, zygotes, and blastocysts and found that the paternally and maternally inherited alleles are treated differently. The paternally inherited allele is demethylated rapidly, and the maternal allele is demethylated more slowly, in a manner similar to that of nonimprinted single-copy genes. Interestingly, following maternal transmission of the allele, there is no DNA methylation in the blastocyst, suggesting that DNA methylation is not the inherited mark. We have independent support for this conclusion from studies that do not involve direct analysis of DNA methylation. Haplo-insufficiency for Mel18, a polycomb group protein, introduces epigenetic inheritance at a paternally derived Avy allele, and the pedigrees reveal that this occurs after zygotic genome activation and, therefore, despite the rapid demethylation of the locus.

There is increasing evidence that epigenetic information can be inherited across generations in mammals, despite extensive reprogramming both in the gametes and in the early developing embryo. One corollary to this is that disrupting the establishment of epigenetic state in the gametes of a parent, as a result of heterozygosity for mutations in genes involved in reprogramming, could affect the phenotype of offspring that do not inherit the mutant allele. Here we show that such effects do occur following paternal inheritance in the mouse. We detected changes to transcription and chromosome ploidy in adult animals. Paternal effects of this type have not been reported previously in mammals and suggest that the untransmitted genotype of male parents can influence the phenotype of their offspring.

Objective The purpose of this study was to investigate the effect of disease modifying therapies on immune response to severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2) vaccines in people with multiple sclerosis (MS). Methods Four hundred seventy‐three people with MS provided one or more dried blood spot samples. Information about coronavirus disease 2019 (COVID‐19) and vaccine history, medical, and drug history were extracted from questionnaires and medical records. Dried blood spots were eluted and tested for antibodies to SARS‐CoV‐2. Antibody titers were partitioned into tertiles with people on no disease modifying therapy as a reference. We calculated the odds ratio of seroconversion (univariate logistic regression) and compared quantitative vaccine response (Kruskal Wallis) following the SARS‐CoV‐2 vaccine according to disease modifying therapy. We used regression modeling to explore the effect of vaccine timing, treatment duration, age, vaccine type, and lymphocyte count on vaccine response. Results Compared to no disease modifying therapy, the use of anti‐CD20 monoclonal antibodies (odds ratio = 0.03, 95% confidence interval [CI] = 0.01–0.06, p < 0.001) and fingolimod (odds ratio = 0.04; 95% CI = 0.01–0.12) were associated with lower seroconversion following the SARS‐CoV‐2 vaccine. All other drugs did not differ significantly from the untreated cohort. Both time since last anti‐CD20 treatment and total time on treatment were significantly associated with the response to the vaccination. The vaccine type significantly predicted seroconversion, but not in those on anti‐CD20 medications. Preliminary data on cellular T‐cell immunity showed 40% of seronegative subjects had measurable anti‐SARS‐CoV‐2 T cell responses. Interpretation Some disease modifying therapies convey risk of attenuated serological response to SARS‐CoV‐2 vaccination in people with MS. We provide recommendations for the practical management of this patient group. ANN NEUROL 2021