Mapping the anatomical and transcriptional landscape of early human fetal ovary development

The complex genetic mechanisms underlying human ovary development can give rise to clinical phenotypes if disrupted, such as Primary Ovarian Insufficiency and Differences of Sex Development. Through a clinically-focused lens, we combine single-nuclei RNA sequencing, bulk RNA sequencing, and micro-focus computed tomography to elucidate the anatomy and transcriptional landscape of the human fetal ovary across key developmental timepoints (Carnegie Stage 22 until 20 weeks post conception). We show the marked growth and distinct morphological changes within the fetal ovary at the critical timepoint of germ cell expansion, and demonstrate that the fetal ovary becomes more transcriptomically distinct from the testis with age. We describe novel ovary developmental pathways, relating to neuroendocrine signalling, energy homeostasis, mitochondrial networks, piRNA processes, and inflammasome regulation. We define transcriptional regulators and candidate genes for meiosis within the developing ovary. Together, this work advances our fundamental understanding of human ovary development and clinical ovarian insufficiency phenotypes. ### Competing Interest Statement The authors have declared no competing interest.