RNAseq of Aging Drosophila ISCs

Tissue homeostasis requires long-term lineage fidelity of somatic stem cells. Whether and how age-related changes in somatic stem cells impact the faithful execution of lineage decisions remains largely unknown. Here, we address this question using genome-wide chromatin accessibility and transcriptome analysis as well as single cell RNA-seq to explore stem cell intrinsic changes in the aging Drosophila intestine. These studies indicate that in stem cells of old flies, promoters of Polycomb (Pc) target genes become differentially accessible, resulting in the increased expression of enteroendocrine (EE) cell specification genes. Consistently, we find age related changes in the composition of the EE progenitor cell population in aging intestines, as well as a significant increase in the proportion of EE-specified ISCs and progenitors in aging flies. We further confirm that Pc-mediated chromatin regulation is a critical determinant of EE cell specification in the Drosophila intestine. Pc is required to maintain expression of stem cell genes while ensuring repression of differentiation and specification genes. Our results identify Pc group proteins as central regulators of lineage identity in the intestinal epithelium and highlight the impact of age-related decline in chromatin regulation on tissue homeostasis. Whole midguts were dissociated into single cells across flies lifespan, covering early adulthood (7 days of age), middle age (30 days of age), old age (60 days) and geriatric age/very old (>70 days) and ISCs were sorted by Fluorescent Activated Cell Sorting (FACS) as we have previously described (Tauc et al., 2014). In short, midguts from flies of WDah; esg-Gal4, UAS-2xEYFP; Su(H)GBE-Gal80, were dissected in 1xPBS, 1% Bovine Serum Albumin (BSA) and dissociated in 0.5% Trypsin-EDTA solution for less than 2h at room temperature (RT), during which dissociated cells were collected periodically every 20-30min, resuspended in 1xPBS, 1%BSA and 2%FBS and kept on ice until sorting. A BD Biosciences FACSAria II flow cytometer cell sorter was used for cell sorting.