Human rDNA Structure, Expression, and Non-Canonical Functions: the Role of Non-Coding Regions

Abstract

The review is dedicated to analyzing and summarizing the data on the part of human genome encoding 45S rRNA. The sequences which seem evolutionary conserved on the first glance astonish one with their variability in structure and a variety of functions on closer examination. The major part of rDNA is non-coding and contains regulatory elements, protein binding sites, pseudogenes, repetitive sequences, and microRNA genes. Ribosomal intergenic spacers are not only in charge with the nucleolus morphology and functioning, namely, the rRNA expression and ribosome biogenesis, but also control nuclear chromatin formation thus mediating cell differentiation. Besides, alterations in the expression of these non-coding regions of rDNA in response to environmental stimuli underlies the keen sense of cell to various types of stressors. Malfunctioning of this process may result in a wide range of pathologies from oncology to neurodegenerative disease and mental illness. Here we observe to-date materials on the structure and transcription of the ribosomal intergenic spacer in humans and its role in rRNA expression, in-born disease development, and cancer.