Using the nematode C. elegans germline as a model system, we previously reported that PUF-8 (a PUF RNA-binding protein) and LIP-1 (a dual-specificity phosphatase) repress sperm fate at 20°C and the dedifferentiation of spermatocytes into mitotic cells (termed "spermatocyte dedifferentiation") at 25°C. Thus, double mutants lacking both PUF-8 and LIP-1 produce excess sperm at 20°C, and their spermatocytes return to mitotically dividing cells via dedifferentiation at 25°C, resulting in germline tumors. To gain insight into the molecular competence for spermatocyte dedifferentiation, we compared the germline phenotypes of three mutant strains – fem-3(q20gf), puf-8(q725; fem-3(q20gf), and puf-8(q725); lip-1(zh15). Both fem-3(q20gf) and puf-8(q725); fem-3(q20gf) mutants produced excess sperm like puf-8(q725); lip-1(zh15) double mutants. Our results show that spermatocyte dedifferentiation was not observed in fem-3(q20gf) mutants, but it was more aggressive in puf-8(q725); lip-1(zh15) than in puf-8(q725); fem-3(q20gf) mutants. These results suggest that MPK-1 (the C. elegans ERK1/2 MAPK ortholog) activation by removing the function of LIP-1 in the absence of PUF-8 promotes spermatocyte dedifferentiation. This idea was confirmed using Resveratrol (RSV), a potential activator of MPK-1 and ERK1/2 in C. elegans and human cells. Notably, spermatocyte dedifferentiation was significantly enhanced by RSV treatment, and its effect was blocked by mpk-1 RNAi. We, therefore, conclude that PUF-8 and MPK-1 are normally required to inhibit spermatocyte dedifferentiation and tumorigenesis. Since these regulators are broadly conserved, we suggest that similar regulatory circuitry may control cellular dedifferentiation and tumorigenesis in other organisms, including humans.