Heterozygous Eif4nif1 Stop Gain Mice Replicate the Primary Ovarian Insufficiency Phenotype

We identified a stop-gain mutation in eIF4ENIF1 in a family in which multiple women developed primary ovarian insufficiency (POI) at approximately age 30 years. We hypothesized that the same mutation in a mouse model would replicate POI. Methods: The Eif4enif1 C57/Bl6 transgenic mouse model contains a floxed exon 10-19 cassette and a conditional knock-in cassette containing exon 10 with the c.1286C>G stop-gain mutation causing familial POI and WT exons 11-19 (Eif4enif1WT/flx). The hybrid offspring of CMV-Cre mice with Eif4enif1WT/flx mice were designated Eif4enif1WT/Δ for simplicity. Follicles were counted in fixed H&E stained ovaries from mice age days 1-5 (primordial and primary follicles), day 10, day 22 (first wave of growing follicles from small preantral to small antral follicles), week 20 (peak fertility), then every 2 months from 10 months to 26 months (follicle exhaustion). Litter frequency, pup number and genotype were recorded. Serum FSH levels were measured by the University of Virginia Ligand Assay and Analysis Core. Results: The heterozygotes have no outward or internal phenotypic differences compared to WT (Eif4enif1WT/flx), with the exception of reproductive organs in females and males. A subset of female heterozygotes (Eif4enif1WT/Δ) had no litters for 20 weeks (2 of 18; 11%). In those with litters, the average length of time between litters was not different but the final litter was earlier (5.6±2.7 vs. 10.5±0.7 months; p=0.02). Heterozygous breeding pair (Eif4enif1WT/Δx Eif4enif1WT/Δ) litter size was 60% of WT litter size (3.9±2.3 vs. 7.2±2.1 pups/litter; 0<0.001). The genotypes were 35% Eif4enif1WT/flx and 65% Eif4enif1WT/Δ, with no homozygotes. The number of follicles in ovaries from Eif4enif1WT/Δ mice was lower starting at the primordial (499±290 vs. 1445±381) and primary follicle stage (1069±346 vs. 1450±193) on day 10 (p<0.05). The preantral follicle number was lower starting on day 21 (213±86 vs. 522±227; p<0.01) and the antral follicle count was lower starting on week 20 (78±38 vs. 119±18; p<0.01). The FSH level in 12-month old mice during estrus was higher in a heterozygote compared to WT (25.0 vs. 12.1 ng/mL). Conclusions: Heterozygous Eif4enif1 stop-gain mutants have follicle loss documented by day 10, decreased pup number with no homozygotes, earlier end of reproductive function and elevated FSH levels. These mice replicate the POI phenotype in women. eIF4ENIF1 regulates protein translation by binding and storing eIF4E bound mRNA. Therefore, the unique mouse model provides a platform to study temporal and spatial regulation of protein translation across oocyte and embryo development in mammals. Further studies will determine whether follicle loss results from premature protein translation in oocytes.