MON-200 - Steroidogenic Factor 1 (NR5A1/SF1) Drives Stage-Specific HERV (Human Endogenous Retroviruses) Reprogramming during Human Testis-Like Differentiation

Background: NR5A1/SF1 is a master regulator of human testis determination. HERVs (human endogenous retroviruses) are ancient retroviral insertions whose loci can be transcribed in specific contexts, making them plausible contributors to gonadal transcriptional programs. Whether NR5A1 activates a stage-specific HERV/LTR program during early human gonadal differentiation—with potential relevance to differences of sex development (DSD)—is unknown.

Methods: We analyzed high-depth bulk RNA-seq from XY hiPSCs differentiated across three developmental stages—pre-bipotential gonad, bipotential gonad, and gonadal-like cell stages (n=3 per condition/stage)—with and without induced NR5A1. Coding genes were quantified with Kallisto and tested with DESeq2. Because ERV/HERV-LTR transcripts often generate multi-mapping reads, locus-specific expression was quantified with Telescope and tested with DESeq2. Differential expression was assessed between NR5A1-induced and non-induced cells within each stage.

Results: NR5A1 induction triggered a marked, stage-dependent remodeling of the ERV/HERV-LTR transcriptome. At |log2FC|>1 and adjusted P< 0.05, 33 ERV loci were differentially expressed (17 up; 16 down) with high stage specificity. Up-regulation was most prominent at the gonadal-like cell stage (11 stage-specific loci). A representative locus, HERV3 at 14q11.2, showed strong NR5A1-associated up-regulation at the pre-bipotential gonad stage (log2FC=9.33; adjusted P=1.03×10⁻²⁰). Coding-gene reprogramming occurred in parallel, while ERV/HERV-LTR changes highlighted a prominent, stage-resolved signature of NR5A1 induction.

Conclusions: NR5A1/SF1 induction is associated with robust, stage-specific ERV/HERV-LTR reprogramming during human testis-like differentiation. These findings implicate ERV loci as prominent NR5A1-responsive features of early human gonadal development and motivate mechanistic studies to define candidate regulatory roles in human testis determination and potential relevance to DSD.

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