Hormones are signal substances formed in the cells of the endocrine glands. After synthesis, hormones enter the blood and are transferred to the target organs, where they perform certain biochemical and physiological regulatory functions.
Hormonal systems are usually interrelated and, in a number of cases, form a hierarchical ladder. The most important of these is the pituitary and hypothalamic hormone system, controlled by the central nervous system (CNS). Steroid hormones act only on target cells and often suppress the synthesis or secretion of other hormones of the regulatory cascade. The most important among the steroid hormones of vertebrates are the sex hormones.
A common precursor of steroid hormones is cholesterol. It comes from different sources into hormone-synthesizing cells of the glands as part of low-density lipoproteins (LDL) or is synthesized in cells from acetyl CoA. Separate stages of the biosynthesis of steroid hormones are catalyzed by highly specific enzymes. Changes in the structure of these enzymes as a result of mutations can cause disturbances in the development of certain functions of the body.
All steroid hormones are lipophilic signaling substances. The site of action of these bioregulators is the nuclei of the target cells. In the blood, lipophilic hormones are usually associated with transport proteins of the blood. However, only the free hormone penetrates through the plasma membrane. In the cytoplasm or in the cell nucleus, the hormone interacts with a specific receptor. Binding of the hormone entails a conformational rearrangement of the receptor protein molecule conjugated with other proteins, dissociation with the release of inhibitor proteins and the formation of dimers with increased affinity for DNA.
A key stage in the hormonal regulation process is the binding of dimers of the hormone receptor complex to double-stranded DNA. The complex binds to regulatory regions of genes that have a specific nucleotide sequence, which is important for maintaining the specificity of the hormonal action. The binding of receptor dimers to GRE leads to stimulation, less often to inhibition, transcription of neighboring genes.
All of the above is of great importance for the determination and differentiation of sex in animals, including birds. At any stage, as a result of mutations of certain genes, violations may occur, and the characteristics of the gender may change. The extreme form of these changes is sex inversion.
The study was conducted with the financial support of the Russian Foundation for Basic Research (Project 17-04-01321a).