The Transcriptome Trajectory Reveals Sex- and Age-Dependent Changes in the Mouse Adrenal Gland

In both humans and mice, the adrenal gland is a sexually dimorphic organ, but the extent of this diversity throughout development remains unclear. Here, we analyzed the mouse adrenal gland transcriptome at postnatal days 0, 7, 15, 21, 28, 35, and 49 to uncover its transcriptomic trajectory. Sex-dependent differences, indicated by the number of differentially expressed genes, gradually increase over time. Two Y-linked genes are consistently expressed in male adrenal glands, suggesting that factors beyond sex hormones may contribute to adrenal sexual dimorphism. Genes involved in steroidogenesis, cholesterol synthesis, and catecholamine synthesis exhibit sex- and age-dependent differential expression. Weighted gene co-expression network analysis (WGCNA) identified many genes with known zone-specific adrenal expression, including Akr1c18, Pik3c2g, Cyp2f2, Dhcr24, Thrb, and Spp1, clustering within the same module. FRZB, a WNT inhibitor, was also part of this module, exhibiting sex- and age-dependent expression. Immunostaining confirmed that FRZB is specifically expressed in the inner cortex, aligning with other inner cortex markers. Additionally, heatmap analysis revealed that many WNT downstream genes show age-dependent increases in expression in males, corresponding to progressively lower Frzb levels, suggesting a regulatory role for Frzb in adrenal sexual dimorphism. Furthermore, collagen-related genes were highlighted in the clustered heatmap of all differentially expressed genes due to their gradual decrease in expression over time. These observations suggest that this comprehensive dataset not only enhances our understanding of adrenal development and sexual dimorphism, aids in identifying novel marker genes for specific adrenal cell types, but also holds potential for contributing to aging research.