Transcriptomic Responses of Zebrafish Embryos to Environmentally Relevant, Low-Dose (2-Ethylhexyl) Phthalate Exposure at 96–120 hpf

Background: Di(2-ethylhexyl) phthalate (DEHP) is a high-production-volume plasticizer and ubiquitous environ-mental contaminant with established endocrine-disrupting potential. While zebrafish transcriptomic studies have typically used high concentrations and long exposure windows, less is known about genome-wide responses during late embryogenesis/early larval maturation under environmentally relevant exposures. Here we profiled whole-organism transcriptomic responses to a short DEHP exposure during a developmentally sensitive transition (96–120) hours post-fertilization, hpf) and interpreted responses using differential expression, enrichment analyses, and endocrine-focused protein–protein interaction (PPI) network modeling. Methods: Wild-type AB zebrafish lar-vae (96 hpf) were exposed to DEHP at 10−9 M or solvent control for 24 h. Larvae were pooled per replicate (25 lar-vae/pool) and processed for poly(A)-selected RNA-seq. Reads were quality-controlled, aligned to the Danio rerio reference genome, and quantified at gene- level. Differential expression was performed using DESeq2. Functional enrichment used KEGG over-representation analysis (ORA) and gene set enrichment analysis (GSEA). Zebrafish genes were mapped to human orthologs for GO/KEGG and STRING-based endocrine subnetworks, which were visualized and interrogated using STRINGdb and visNetwork. Results: Low-dose, short-term exposure does not produce large gene-level effects but induces coordinated, pathway-level transcriptional remodeling. KEGG ORA showed significant enrichment of MAPK signaling and regulation of actin cytoskeleton with additional enrichment of axon guidance and neuroactive ligand–receptor interaction. GSEA detected coordinated downregulation of KEGG neurodegeneration collections with negative normalized enrichment scores reflecting shared gene sets re-lated to mitochondrial function, proteostasis, cytoskeletal organization, and stress-response pathways. Endo-crine-focused STRING subnetworks indicated consistent downregulation of CYP19A1 within estrogen metabo-lism/biosynthesis modules and downregulation of upstream androgen biosynthetic enzymes HSD3B2 and CYP17A1, alongside upregulation of HSD17B3 and proteostasis-associated factors including DNAJA1. Endocrine network to-pology highlighted regulatory and cofactor nodes affecting receptor-linked transcription, consistent with indirect endocrine modulation rather than large receptor-transcript changes. Conclusions: In summary, this study demon-strates that exposure to low-dose DEHP during a critical period of zebrafish embryonic development is associated with modest but coordinated transcriptomic changes across multiple biological pathways. Pathway enrichment and network-based analyses highlight estrogen- and androgen-associated processes, along with broader signaling, met-abolic, and structural pathways, as transcriptionally responsive during this window. Importantly, these findings reflect molecular-level associations rather than direct evidence of functional or physiological endocrine disruption. Instead, they identify candidate pathways and regulatory networks that may be sensitive to low-level environmen-tal exposure and warrant further investigation. Collectively, this work underscores the value of systems-level tran-scriptomic approaches for detecting subtle, pathway-wide responses to environmentally relevant exposures during development.