Mechanics of oogenesis: Lessons from C. elegans germline cysts

Germ cells are organized into a syncytial architecture, wherein individual cells remain connected via intercellular bridges. Within this structural framework, known as germline cysts, a subset of germ cells enlarges and develops into oocytes, while others shrink and are eliminated through cell death. Recent studies with Caenorhabditis elegans have revealed that both apoptosis-mediated germ cell death and enlargement of surviving germ cells are regulated by mechanical forces. Germ cells exhibit stochastic fluctuations in volume driven by actomyosin contractility. This initial size heterogeneity is progressively amplified due to mechanical instability driven by differential hydrostatic pressure within the cyst, which biases smaller cells toward shrinkage and subsequent apoptotic death. This mechanical instability is further reinforced by the RAS/MAPK signaling cascade and the ECT-2/RhoA pathway, both of which enhance actomyosin contractility. Surviving germ cells continue to grow by acquiring the cytoplasmic materials through actomyosin contractility-mediated hydrodynamic flow within the cyst. Collectively, these findings highlight the critical role of mechanical forces in modulating cell fate decisions between survival and death, facilitating cell volume dynamics and maintaining germline homeostasis during oogenesis.