Histone demethylase that specifically demethylates trimethylated 'Lys-27' of histone H3, a mark associated with transcriptional repression, thereby playing a central role in the histone code (PubMed:17713478, PubMed:25124442). Involved in the transcriptional regulation of the heat shock response, unfolded protein response and possibly other stress response target genes (PubMed:26212459,PubMed:27133168). Required for gonad development and organization (PubMed:17713478). Required for the robust transdifferentiation of the Y rectal epithelial cell to the PDA motor neuron during larval development (PubMed:25124442). Acts cell-autonomously in Y-to-PDA transdifferentiation, which depends on the demethylase activity and on recognition of the H3 tail (PubMed:25124442). Cooperates with set-2 and unc-3 to ensure robust Y-to-PDA transdifferentiation (PubMed:25124442). Promotes mitochondrial stress-induced longevity (PubMed:27133168). Involved in lifespan regulation (PubMed:21803287, PubMed:26212459). Interacts with wdr-5.1 and unc-3. Mainly expressed in head and tail. Expressed in the Y cell before transdifferentiation in the embryo and during redifferentiation into the PDA neuron in larval stages L2 and L3 but not in larval stage L1 (PubMed:25124442). Expression declines in the adult soma (PubMed:26212459). RNAi-mediated knockdown results in abnormal gonad migration with aberrant turns and positioning of the distal end as well as in disorganized accumulation of oocytes in the proximal gonad arm (PubMed:17713478). RNAi-mediated knockdown also results in disruption of invariant Y-to-PDA transdifferentiation (PubMed:25124442). RNAi-mediated knockdown suppresses mitochondrial stress response mediated longevity (PubMed:27133168). RNAi-mediated knockdown reduces lifespan of floxuridine-treated animals (PubMed:21803287). Belongs to the UTX family.