(A) Violin plots depicting normalized counts for YTHDC2, MEIOC, and XRN1 in the developing ovary and testis at 4 developmental stages (4 samples at stages CS22/23, 9 wpc, 11 wpc, 15/16 wpc). (B) Quantitative reverse transcriptase PCR (qRT-PCR) expression (log₂) of YTHDC2 in developing ovary and testis compared with reference (ACTB) and relative to expression in an index CS22 ovary sample. Four fetal ovary and fetal testis samples were included at CS22/CS23, 9 wpc, 11 wpc, 15/16 wpc, and 19/20 wpc. (C) qRT-PCR expression (log₂) of MEIOC in developing ovary and testis compared with reference (ACTB) and relative to the expression in a CS22 ovary sample. Four fetal ovary and fetal testis samples were included at CS22/CS23, 9 wpc, 11 wpc, 15/16 wpc, and 19/20 wpc. (D) qRT-PCR mean expression (log₂) of YTHDC2 in 4 adult ovary samples and 4 adult testis samples from individuals without gonadal insufficiency. B–D represent mean expression of triplicates, and error bars indicate mean ± SEM. qRT-PCR experiments were performed 3 times; representative data from 1 experiment shown. Differences in mean expression between sample groups were assessed using multiple t test analysis (*P < 0.05; **P < 0.01); correction for multiple comparisons was performed using Holm-Šídák. CS, Carnegie stage. (E) Uniform manifold approximation and projection representation of distinct germ cell clusters (n = 8867 germ cells) identified by single-cell RNA sequencing of human fetal gonads between 6 and 21 wpc. Key ovary clusters are annotated. PGCs, primordial germ cells; GCs, germ cells. (F) Visium spatial transcriptomic expression of YTHDC2 in a 17 wpc human fetal ovary. EG, extragonadal. (G) Immunohistochemistry of YTHDC2 in a 16 wpc human fetal ovary showing increased staining in the central region containing meiotic cells and decreased staining in primordial germ cells at the periphery in the cortex of the fetal ovary (PGCs).