Highlights d Genome-wide resource for genetic mosaic analysis with double markers in mice d Resource for dissection of cell-autonomous gene function of >96% of the mouse genome d Resource for genome-wide analysis of genomic imprinting phenotypes d MADM chromosomes reveal non-random mitotic sister chromatid segregation in vivo

Mosaic Analysis with Double Markers (MADM) offers a unique approach to visualize and concomitantly manipulate genetically-defined cells in mice with single-cell resolution. MADM applications include the analysis of lineage; single-cell morphology and physiology; genomic imprinting phenotypes; and dissection of cell-autonomous gene functions in vivo in health and disease. Yet, MADM could only be applied to <25% of all mouse genes on select chromosomes thus far. To overcome this limitation, we generated transgenic mice with knocked-in MADM cassettes near the centromeres of all 19 autosomes and validated their use across organs. With this resource, >96% of the entire mouse genome can now be subjected to single-cell genetic mosaic analysis. Beyond proof-of-principle, we applied our MADM library to systematically trace sister chromatid segregation in distinct mitotic cell lineages. We found striking chromosome-specific biases in segregation patterns, reflecting a putative mechanism for the asymmetric segregation of genetic determinants in somatic stem cell division.

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Intermittent fasting (IF) is a promising non-pharmacological strategy to counteract ageing which has been shown to increase the number of adult-born neurons in the dentate gyrus of mice. However, it is still unclear which steps of the adult neurogenesis process are regulated by IF. The number of adult neural stem cells (NSCs) decreases with age in an activation-dependent manner. To counteract the loss of the stem cell pool, adult NSCs are mostly found in an inactive, quiescent state which ensures their long-term maintenance. We aimed to determine if and how IF impacts the activity and maintenance of adult NSCs in the hippocampus. We chose an every-other-day fasting protocol with food re-administration at night, which we found effectively induces fasting features and preserves the circadian activity pattern of mice. To determine the effects of IF on NSCs and all following steps in the neurogenic lineage, we combined fasting with lineage tracing and label retention assays. We found that IF does not affect NSC activation or maintenance. Contrary to previous reports, we also found that IF does not increase hippocampal neurogenesis. We obtained the same results regardless of strain, sex, diet length, tamoxifen administration or new-born neuron identification method. Our data suggest that NSCs maintain homeostasis upon IF and that this intervention is not a reliable strategy to increase adult neurogenesis.