Sexually Dimorphic Gene Expression in Mammalian Somatic Tissue

Background: The sexually dimorphic differentiation of the bipotential gonad into testis or ovary initiates the sexually dimorphic development of mammals and leads to divergent hormone concentrations between the sexes throughout life. However, despite the fact that anatomic and hormonal differences between the sexes are well described, only a few studies have investigated the manifestation of these differences at the transcriptional level in mammalian somatic tissue. Objective: This review focuses on basic regulatory mechanisms of sex-specific gene expression and examines recent gene expression profiling studies to outline basic differences between the sexes at the transcriptome level in somatic tissues. Methods: To identify gene expression profiling studies addressing sexually dimorphic gene expression, the PubMed database was searched using the terms sex* and dimorp* and gene expression not drosophila not elegans. Abstracts of all identified publications were screened for studies explicitly using microarrays to identify sex differences in somatic tissues of rodents or humans. The search was restricted to English-language articles published in the past 5 years. Reference lists of identified articles as well as microarray databases (Gene Expression Omnibus and ArrayExpress) were also used. Results: The application of microarray technology has enabled the systematic assessment of sex-biased gene expression on the transcriptome level, indicating that the regulatory pathways underlying sexual differentiation give rise to extensive differences in somatic gene expression across organisms. Conclusion: Sustainable annotation of sex-biased gene expression provides a key to understanding basic physiological differences between healthy males and females as well as those with diseases.