ESPE Yearbook of Paediatric Endocrinology

Nature. 2025;643, 262–270 doi: 10.1038/s41586-025-09063-2

Brief summary: This study explored the critical link between iron metabolism and male sex determination in mice, focusing on how iron-dependent epigenetic regulation activates the Sry gene, a key determinant of testis development.

In mice, Sry is expressed in NR5A1⁺ pre-Sertoli cells between embryonic days (E) 10.5 and 12.5, where the histone demethylase KDM3A removes repressive H3K9me2 marks to activate its transcription. Since KDM3A requires Fe²⁺ to function, the authors investigated whether iron metabolism influences this process. Using mouse and human single-cell RNA sequencing, they found that genes involved in iron uptake (e.g., Tfrc, Scara5) and Fe²⁺ production (e.g., Steap3, Ncoa4, Hmox1) are highly enriched in NR5A1⁺ pre-Sertoli cells. Protein and imaging analyses confirmed that these cells accumulate labile iron at E11.5, and iron quantification showed significantly higher iron content in gonadal somatic cells than in surrounding tissues.

To test functional relevance, the authors deleted Tfrc (encoding the iron transporter TFR1) in gonadal somatic cells. Loss of TFR1 reduced Fe²⁺ levels, elevated H3K9me2 marks at the Sry promoter, and halved Sry expression. Despite normal somatic cell numbers, chromatin immunoprecipitation revealed failed H3K9me2 demethylation, linking TFR1-mediated iron uptake to KDM3A activity and Sry activation. Functionally, this impaired male development; many XY embryos lacking Tfrc developed ovaries or ovotestes, mimicking Kdm3a-knockout phenotypes. Ex vivo gonad culture experiments confirmed that iron depletion using deferoxamine (DFO) reduced Sry expression and promoted ovarian characteristics in XY gonads. This effect was reversed by iron supplementation or enforced Sry expression. DFO-treated gonads showed increased H3K9me2 levels at the Sry locus, supporting the need for iron in KDM3A-mediated epigenetic activation. In vivo, maternal iron deficiency, induced via deferasirox (DFX) or a low-iron diet, decreased Sry expression and male-to-female sex reversal, especially in genetically sensitized embryos (e.g., Kdm3a heterozygotes).

Although Kdm3a expression appeared upregulated under iron-deficient conditions, the mechanism remains unresolved. While the results are based on mouse models, they suggest iron is essential for proper epigenetic control during testis determination. This study introduces maternal iron status as a potentially modifiable environmental factor contributing to DSDs, emphasizing the broader developmental importance of micronutrient availability during pregnancy.