# Uridine 5’-monophosphate (UMP) synthesis connects nucleotide metabolism to programmed cell death in C. elegans

## TL;DR

This study shows how UMP synthesis and cell division control apoptosis in C. elegans.

## Contribution

It identifies pyr-1 as a key regulator linking UMP metabolism to programmed cell death.

## Key findings

- UMP availability is essential for PYR-1-mediated programmed cell death.
- Disruption of ACD and PCD leads to extra hypodermal cells and aberrant survival.
- Autophagy and hsp-6 protect against cell death in pyr-1; grp-1 double mutants.

## Abstract

Nucleotide metabolism is essential for fundamental cellular functions such as growth, repair and proliferation. Emerging evidence suggests that metabolic pathways also influence programmed cell death (PCD), though the underlying mechanisms remain poorly understood. One model organism that has provided key insights into the regulation of PCD is Caenorhabditis elegans (C. elegans). In this nematode, apoptosis is often initiated through asymmetric cell division (ACD), a process that unequally distributes fate determinants between daughter cells to produce a larger surviving cell and a smaller cell destined for apoptosis. Here, we demonstrate that the simultaneous disruption of PCD and ACD leads to aberrant cell survival and the formation of extra hypodermal cells. Through a genetic screen in the grp-1 ACD mutant background, we identified pyr-1 as a regulator of PCD. pyr-1 encodes the C. elegans carbamoyl-phosphate synthetase/aspartate transcarbamoylase/dihydroorotase (CAD) enzyme which catalyzes the rate-limiting step of de novo pyrimidine biosynthesis, producing uridine 5’-monophosphate (UMP). UMP is a critical metabolite for the synthesis of nucleotides, lipids and carbohydrates. Genetic analysis of UMP metabolic pathways, combined with exogenous nucleoside supplementation, confirms that UMP availability is essential for PYR-1-mediated PCD. Loss of grp-1 induces cellular stress by disrupting fate determinant partitioning during ACD, whereas pyr-1 mutations cause metabolic stress through UMP depletion. While both mutations independently activate autophagy, they function redundantly to upregulate the mitochondrial chaperone hsp-6. Knockdown of autophagy-related genes and hsp-6 reveals that these pathways serve as compensatory mechanisms to protect against cell death in the pyr-1; grp-1 double mutants. Collectively, our findings establish a direct link between metabolism and cell death, demonstrating how UMP availability and proper ACD coordinate apoptotic regulation and developmental outcomes. This study highlights the intricate interplay between metabolic homeostasis and PCD, providing new insights into the metabolic control of cell fate decisions.