Germ Granules in Animal Oogenesis

Abstract

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.

RNA Helicase Vasa as a Multifunctional Conservative Regulator of Gametogenesis in Eukaryotes

“…In fetal oocytes at the age of 35 weeks, Vasa demonstrates a heterogeneous intracellular distribution: in addition to diffuse staining of the cytoplasm, it is also detected in the granular material located around the nucleus. This arrangement corresponds to Balbiani bodies, which were originally described as germinal complexes consisting of mitochondria, endoplasmic reticulum, and lamellar aggregates and are now considered nuage-related germinal structures [45,185,186]. In some oocytes, Vasa is not associated with the Balbiani bodies, despite having a perinuclear localization in granules.…”

“…Thus, biomolecular condensates partially exclude the aqueous phase [43,44]. The phase separation of proteins is mainly due to weak electrostatic, hydrophobic, π-cationic, cation-cationic, and π-π interactions between neighboring molecules and can be achieved through the interaction of certain domains and the presence of extended regions of intrinsic disorders [43,45]. Intrinsically disordered regions (IDRs) have no defined tertiary structure but contain low-complexity amino acid sequences that can participate in the formation of dynamic multivalent networks that appear in vivo and in vitro as phase-separated droplets [42][43][44].…”