Mikhail A. Dobrynin

In eukaryotic cells, many macromolecules are organized as membraneless biomolecular condensates (or biocondensates). Liquid–liquid and liquid–solid phase transitions are the drivers of the condensation process. The absence of membrane borders makes biocondensates very flexible in their composition and functions, which vary in different cells and tissues. Some biocondensates are specific for germ line cells and are, thus, termed germ granules. This review summarizes the recent data on the composition of germ granules and their functions in gametes. According to these data, germ granules are involved in the determination of germline cells in some animals, such as Amphibia. In other animals, such as Mammalia, germ granules are involved in the processes of transposons inactivation and sequestration of mRNA and proteins to temporarily decrease their activity. The new data on germ granules composition and functions sheds light on germ cell differentiation and maturation properties.

Tandemly repeated pericentromeric noncoding DNA (TR DNA) makes up approximately 10% of the human genome. Pericentromeric TR DNA includes classical human satellites 1, 2, 3 (HS1, HS2, HS3), which are transcribed in somatic cells. We have previously shown the presence of HS2/HS3 transcripts in late human oogenesis and sequenced them. It has been suggested that the RNPs found may be the site of spatial sequestration of RNA and proteins at the end of human oocytes maturation. The aim of this work was to develop a method for inactivating HS2/HS3 transcripts using antisense oligonucleotides to assess its effect on the size and quantity of DDX4-containing RNPs in late human oogenesis. Inactivation of HS2/HS3 transcription at the end of human oocytes maturation by the microinjection method resulted in a significant decrease of the total HS2/HS3 RNA signal, detected by the method of fluorescence in situ hybridization (FISH). At the same time, an increase in the number of inclusions positive to antibodies to RNA helicase DDX4 was observed. Supposedly, upon inactivation of HS2/HS3 transcription, dissociation of DDX4-containing RNP particles occurred. Such changes of the RNP particles can play a critical role in the development of oocytes and be a cause of the arrest of maturation or the occurrence of pathological syndromes, including those associated with problems of fertilization.