Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus.
Authors: Scarlet Dragos, Handschuh Stephan, Reichart Ursula, Podico Giorgia, Ellerbrock Robyn E, Demyda-Peyrás Sebastián, Canisso Igor F, Walter Ingrid, Aurich Christine
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus Between days 45 and 60 of gestation, the equine fetus undergoes critical gonadal development that establishes the foundation for reproductive function throughout life. Researchers used advanced imaging (micro-computed tomography) combined with immunohistochemistry and multiplex immunofluorescence to map gonadal development and track primordial germ cell (PGC) migration and distribution across this narrow developmental window. Fetal gonads expanded dramatically—23-fold across the study period—with sex-specific differences emerging early: testicular tissue showed organised tubular structures from day 50 onwards and expressed strong anti-Müllerian hormone (AMH), whilst ovarian tissue remained composed of cell clusters and lacked AMH expression. PGCs were actively migrating into the gonads by day 45 but had completed their migration by day 60, with approximately 85% of PGCs in both sexes maintaining pluripotency markers (CD117), though only 3–8% were actively dividing at this stage. These findings demonstrate that sexual differentiation in horses begins before day 45—earlier than previously characterised—and progresses along distinctly different trajectories depending on fetal sex, which has implications for understanding reproductive disorders and the developmental origins of breeding soundness in foals.
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Practical Takeaways
- •Sexual differentiation in horse fetuses occurs asynchronously between sexes and begins before day 45 of gestation, relevant for understanding reproductive developmental abnormalities
- •The characterization of primordial germ cell markers (LIN28, CD117, Ki67) provides baseline data for investigating fertility issues or gonadal dysgenesis in foals
- •Knowledge of gonadal development timing may inform management of pregnant mares and prediction of reproductive competence in offspring
Key Findings
- •Fetal gonads increased 23-fold in size between days 45-60 of gestation, with tubular structures present in testes from day 50 onwards and cell clusters dominating in ovaries
- •AMH expression was strong in fetal testes but absent in ovaries, indicating sex-specific differentiation
- •Primordial germ cell migration from mesonephros to gonad occurred at day 45 but not at day 60, with number and distribution influenced by fetal sex (p < 0.05)
- •Most primordial germ cells (84.6-86.8%) were pluripotent based on CD117 co-localization, but only 3.2-7.5% were proliferating based on Ki67 expression