Munoa-Hoyos, I. | bioRxiv Science

bioRxiv2026

Chronic morphine treatment induces a conserved Smchd1-dependent epigenetic memory that disrupts X-chromosome inactivation and genomic imprinting

Epigenetic memory ensures stable inheritance of gene expression patterns critical for embryonic development. Environmental exposures can disrupt this memory, yet the mechanisms remain unclear. Here we demonstrate that chronic morphine exposure induces a persistent transcriptomic and epigenetic memory by repressing Smchd1, a key chromatin regulator, in mouse embryonic stem cells, preimplantation embryos, and human induced pluripotent stem cells. This repression compromises maintenance of X-chromosome inactivation and genomic imprinting, leading to sustained dysregulation of developmentally important gene clusters. Morphine-induced epigenetic alterations also involve changes in DNA methylation and histone modifications along the X chromosome and notably increased H3K27me3 at the Smchd1 locus. These findings reveal a conserved mechanism by which opioid exposure disrupts higher-order chromatin architecture and epigenetic memory during early development, potentially contributing to long-term developmental and clinical outcomes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=97 SRC="FIGDIR/small/713629v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@16986cborg.highwire.dtl.DTLVardef@1108eaaorg.highwire.dtl.DTLVardef@66373org.highwire.dtl.DTLVardef@16b37f6_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2025

Chronic morphine treatment leads to a global DNA hypomethylation via active and passive demethylation mechanisms in mESCs

Epigenetic changes are essential for normal development and ageing, but there is still limited understanding of how environmental factors can cause epigenetic changes that leads to health problems or diseases. Morphine is known to pass through the placental barrier and impact normal embryo development by affecting the neural tube, frontal cortex and spinal cord development, and, as a consequence, delaying nervous system development. In fact, in-utero morphine exposure has shown alterations in anxiety-like behaviours, analgesic tolerance, synaptic plasticity and the neuronal structure of offspring. However, how morphine leads to abnormal neurogenesis and other physiological consequences during embryo development is still unknown. Considering that DNA methylation is a key epigenetic factor crucial for embryo development, our aim is to elucidate the role of methylation in response to morphine. Chronic morphine treatment (24h, 10M) induces a global hypomethylation in mESC. WGBSeq identifies 16,808 sensitive to morphine which are involved in embryo development, signalling pathways, metabolism and/or gene expression, suggesting that morphine might impact methylation levels at developmental genes. Integrative analyses between WGBSeq and RNASeq identified Tet1 as morphine-sensitive gene. Morphine increased the gene expression of Tet1, modifying the methylation levels at the promoter. On the other hand, RNASeq and qRT-PCR analyses revealed that Dnmt1 gene expression decreased after morphine treatment, without altering the methylation patter at its promoters. By MS/MS approaches confirms a decrease in DNA methylation after chronic morphine treatment, together with an increase in hydroxymethylation global levels in mESCs. In conclusion, morphine induces a global hypomethylation in mESC through different mechanisms that involves passive demethylation and a self-regulatory mechanism via active demethylation. One Sentence SummaryUnderstanding how environmental epigenetics impact on embryo development aids to unravel changes that leads to health problems or diseases in the adulthood. Graphical abstractChronic morphine treatment induces a global hypomethylation in mESC through different mechanisms that involves passive demethylation and a self-regulatory mechanism via active demethylation in genes involved in embryo development. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=138 SRC="FIGDIR/small/643512v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@e9d286org.highwire.dtl.DTLVardef@fc7066org.highwire.dtl.DTLVardef@1374039org.highwire.dtl.DTLVardef@598f05_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗