Unsaturated fatty acids are required for germline proliferation and membrane structural integrity in <i>Caenorhabditis elegans</i>

Unsaturated fatty acids (UFAs) are critical components of membrane lipids, but their specific roles in germline development and reproductive health remain poorly defined. Here, we investigated the consequences of UFA depletion in the Caenorhabditis elegans germline using an auxin-inducible degron (AID) system to conditionally degrade FAT-7, the major Δ9 stearoyl-CoA desaturase, in a fat-5; fat-6 double mutant background. This strategy bypassed the lethality associated with complete loss of Δ9 desaturase activity, enabling analysis of UFA deficiency in adult animals. UFA depletion led to a dramatic reduction in brood size, elevated embryonic and larval lethality, and a severe loss of germline nuclei. We found that UFAs are essential for mitotic proliferation, DNA replication, and chromosome organization in the germline. Moreover, reduced UFA levels impaired meiotic progression, accompanied by loss of membrane integrity in the syncytial germline. Notably, UFA deficiency altered the spatial distribution and increased the signal intensity of nuclear pore complex (NPC) proteins, suggesting alterations to the nuclear envelope (NE). Together, our findings demonstrate that UFAs are indispensable for germline maintenance, affecting cell cycle progression, chromosome organization, and membrane architecture. These results underscore a fundamental link between acyl chain composition and reproductive success, highlighting the critical role of lipid homeostasis in the germline.