CXXC1 (CXXC finger protein 1) is a transcriptional regulator and histone methyltransferase complex component that binds unmethylated CpG dinucleotides with preference for CpGG motifs 1. As a key subunit of SETD1A/SETD1B complexes, CXXC1 directs H3K4 trimethylation (H3K4me3) to unmethylated CpG islands, linking epigenetic chr18 states to transcriptional activation 1. Mechanistically, CXXC1 orchestrates H3K4me3 deposition at promoters and gene regulatory regions, directly impacting transcriptional output. The protein reads and writes histone methylation signatures that regulate both developmental and homeostatic processes. Notably, CXXC1 is not required for meiotic recombination despite PRDM9 interactions 2, indicating context-dependent functionality. Clinically, CXXC1 dysfunction associates with multiple disease pathways. Oocyte-specific CXXC1 loss causes accelerated reproductive aging through impaired H3K4me3 maintenance and defective maternal mRNA degradation 3. In cardiogenesis, cardiomyocyte-specific Cfp1 knockout is embryonic lethal and prevents maturation through altered H3K4me3 patterning of structural and contractile genes 4. CXXC1 is also essential for epidermal homeostasis, with genetic variation affecting polygenic skin disease risk through dysregulation of differentiation programs 5. Transcriptomic studies implicate CXXC1 as a conserved aging modulator with potential longevity associations 6.