Stochastic gene expression leads to inherent variability in expression outcomes even in isogenic single-celled organisms grown in the same environment. The Drop-Seq technology facilitates transcriptomic studies of individual mammalian cells, and it has had transformative effects on the characterization of cell identity and function based on single-cell transcript counts. However, application of this technology to organisms with different cell size and morphology characteristics has been challenging. Here we present yeastDrop-Seq, a yeast-optimized platform for quantifying the number of distinct mRNA molecules in a cell-specific manner in individual yeast cells. Using yeastDrop-Seq, we measured the transcriptomic impact of the lifespan-extending compound mycophenolic acid and its epistatic agent guanine. Each treatment condition had a distinct transcriptomic footprint on isogenic yeast cells as indicated by distinct clustering with clear separations among the different groups. The yeastDrop-Seq platform facilitates transcriptomic profiling of yeast cells for basic science and biotechnology applications.

SUMMARYAlthough double-strand break (DSB) repair is essential for a cell’s survival, little is known about how DSB repair mechanisms are affected by age. Here we characterize the impact of cellular aging on the efficiency of single-strand annealing (SSA), a DSB repair mechanism. We measure SSA repair efficiency in young and old yeast cells and report a 23.4% decline in repair efficiency. This decline is not due to increased use of non-homologous end joining. Instead, we identify increased G1 phase duration in old cells as a factor responsible for the decreased SSA repair efficiency. Expression of 3xCLN2 leads to higher SSA repair efficiency in old cells compared with expression of 1xCLN2, confirming the involvement of cell-cycle regulation in age-associated repair inefficiency. Examining how SSA repair efficiency is affected by sequence heterology, we find that heteroduplex rejection remains high in old cells. Our work provides insights into the links between single-cell aging and DSB repair efficiency.

In addition, the page numbers provided in references 15 and 16 were incorrectly given as 316689 -331700 and 294 -319, respectively. The correct page numbers are 31689-31700 (reference 15) and e00294-19 (reference 16).

Aging, the time-dependent accumulation of molecular damage, is the primary limiting factor of human lifespan. Slowing down damage accumulation or its prevention therefore represents a promising therapeutic paradigm to combat aging-related disease and death. While several chemical compounds extend lifespan in model organisms, their mechanism of action is often unknown, reducing their therapeutic potential. Using a systematic approach, here we show that inhibition of GMP synthesis is a novel lifespan extension mechanism in yeast. We further discover that proteasome activation extends lifespan in part through GMP insufficiency. GMP synthesis inhibition exerts its lifespan extension effect independently of the canonical nutrient-sensing and sirtuin pathways regulating lifespan. Exposing longitudinally aging yeast cells to GMP synthesis inhibition in an age-dependent manner, we demonstrate that the lifespan extension by GMP insufficiency is facilitated by slowing, rather than reversing, the aging process in cells. While GMP and its downstream metabolites are involved in many cellular processes in cells, our results rule out the combined effect of global transcription and translation on cellular lifespan. These findings elucidate the involvement of nucleotide metabolism in the aging process. The existence of clinically-approved GMP synthesis inhibitors elicits the potential of a new class of therapeutics for aging-related disorders.