C. elegans Reproductive Aneuploidy

C. elegans generally reproduce as hermaphrodites, generating sperm during larval development and using those sperm to fertilize oocytes generated during adulthood, a process resulting in low embryo lethality and clonal hermaphroditic offspring. In oocytes, aging and exposure to stressors, including heat and X-irradiation, increase the rate of nondisjunction on the X chromosome, which, upon fertilization, results in increased numbers of aneuploid progeny, which are male and reproduce sexually by mating with hermaphrodites of the same or different genetic backgrounds (57 (link), 58 (link)). Notably, loss-of-function alleles in many meiotic genes result in a high incidence of males among the progeny, called the “him” phenotype (11 (link), 59 (link)). Analysis of these mutants led to identification of genes governing critical stages of chromosomal segregation and DNA repair during meiosis (19 –22 (link)). Aging, stressors, and many him mutants also induce aneuploidy on autosomes, which results in dead embryos. Males are distinguished from the hermaphrodites by their distinct body shape and tail structure (11 (link)). Male percentage in a brood was calculated as (number of males/total live progeny counted) × 100. An egg/embryo was judged as dead if it failed to hatch after more than 24 hours. Dead embryo frequency was then calculated as (number of dead embryos/total embryos laid) × 100, where total embryos equaled live progeny plus dead embryos. Because males and dead embryos without stressors were relatively rare events, their values were enumerated and presented as combined value from all replicates of all independent experiments showing similar trends. Data involving stressor-induced dead embryos in C. elegans where the frequency is higher are presented as values from individual replicates of the experiment, and 95% confidence intervals presented show the extent of inter-replicate variability when data from independent experiments were combined.