The KMT2D (MLL4)-ASCOM and KMT2C (MLL3)-ASCOM complexes methylate H3K4 at nucleosomes of PPARG target genes during adipogenesis, thus creating an active chromatin mark. A flavonoid, kaempferol, is a PPARG antagonist that prevents rosiglitazone-induced association of Mll4 with Pparg at Pparg target loci and H3K4 methylation of nucleosomes associated with Pparg targets in mouse adipocytes (Park et al. 2022). As MLL3 and MLL4 mostly function as H3K4 monomethyl transferases, histone modifications at all target gene loci are shown as monomethylation (H3K4me1). At some target loci other types of H3K4 methylation (di- and trimethylation) have been reported, as indicated below. KMT2C/KMT2D-dependent H3K4 methylation has been shown at the following PPARG target genes:

CD36 gene (Kim et al. 2016: MLL4-dependent increase in H3K4me1 levels coincident with PPARG and KMT2D recruitment to regulatory gene elements was detected in steatotic mouse hepatocytes)

CEBPA gene (Cho et al. 2009: H3K4me3 signal at the CEBPA proximal promoter is reduced upon deletion of PAXIP1 - PTIP - in mouse embryonic fibroblasts - MEFs; in mouse white preadipocyte line 3T3-L1; H3K4me3 is enriched around the transcription start sites of CEBPA before and after the onset of differentiation; in differentiating mouse brown preadipocytes, H3K4me3 is enriched around the transcription start site of CEBPA in a PAXIP1-dependent manner)

CIDEC gene (Kim et al. 2016: KMT2D-dependent increase in H3K4me1 levels coincident with PPARG and KMT2D recruitment to regulatory gene elements was detected in steatotic mouse hepatocytes)

FABP4 gene (Lee et al. 2008: the kinetics of H3K4 trimethylation at the mouse FABP4 gene locus corresponds to the kinetics of KMT2C/KMT2D recruitment, and is followed by H3 and H4 acetylation; PPARG ligand rosiglitazone induced H3K4 trimethylation in MEFs which was abolished in NCOA6 null cells and significantly attenuated in Kmt2c delta/delta MEFs that express catalytically inactive KMT2C)

PPARG (Cho et al. 2009: in MEFs, which only express PPARG1 but not PPARG2 isoform of PPARG, increased trimethylation of the PPARG1 proximal promoter at H3K4 - H3K4me3 mark of active chromatin - was dependent on the presence of PAXIP1 (PTIP), an accessory subunit of MLL3 and MLL4 complexes; in mouse white preadipocyte line 3T3-L1, H3K4me3 is enriched around the transcription start sites of PPARG1 and PPARG2 before and after the onset of differentiation; in differentiating mouse brown preadipocytes, H3K4me3 is enriched around the transcription start sites of PPARG1 and PPARG2 in a PAXIP1-dependent manner)

SCD gene (Kim et al. 2016: KMT2D-dependent increase in H3K4me1 levels coincident with PPARG and KMT2D recruitment to regulatory gene elements was detected in steatotic mouse hepatocytes)

Targeted knock-in of Kmt2d (Mll4) mutant with deleted SET domain in somatic precursor cells of brown adipose tissue and skeletal muscle leads to death immediately after birth due to breathing malfunction, with affected mice showing similar brown adipose tissue mass but altered morphology and reduced muscle mass compared to wild type mice (Jang et al. 2019). When targeted knock-in involves both Kmt2c (Mll3) and Kmt2d mutants with deleted SET domains, affected mice also die immediately after birth, but show a profound reduction in brown adipose tissue and muscle mass (Jang et al. 2019). Deletion of SET domains in Kmt2c and Kmt2d decreases global levels of H3K4me1 and H3K4me2 but not H3K4me3 in mouse brown preadipocytes (Jang et al. 2019). Deletion of Kmt2c and Kmt2d SET domains reduces protein levels of Kmt2c, Kmt2d, and the accessory protein of Mll3/Mll4 complexes Utx (Kdm6a), but not Rbbp5 - an obligatory subunit of all KMT2 (MLL) complexes (Jang et al. 2019).

While KMT2C/KMT2D-mediated H3K4 methylation of the nucleosomes at regulatory elements of PPARG target genes ACSL1, ACSS3, ADIPOQ, AGPAT2, ANGPTL4, DGAT2, ELOVL5, GPAM, LIPE, LPIN1, LPL, MGLL, PDK4, PEX11A, PLIN1, PLIN2, PLIN4, PNPLA2, SCD5, THRSP has not been reported, the expression of these genes, as well as the genes for which more direct evidence was available (CD36, CEBPA, CIDEC, FABP4, PPARG, and SCD), is severely reduced in differentiating mouse brown preadipocytes expressing histone H3.3 K4M mutant or Kmt2c and Kmt2d with deleted SET domains (Jang et al. 2019: RNA seq, supplementary information).