The oocyte/zygote of drosophila and nematode as a model of evolutionary conservative processes in the early development of mammals and humans

Understanding the molecular mechanisms of oocyte maturation, as well as early embryonic development, is of fundamental importance not only for embryology, but also for medical biology. However, the difficulties of experimental studies of this kind of problems in mammals, and especially in humans, are obvious. It is also well known that many key processes and mechanisms of oogenesis — early embryogenesis are highly evolutionarily conserved. They can be traced from the level of the most studied model invertebrates, such as Drosophila D. melanogaster and roundworm C. elegans, to mammals and humans. In this review, using these model invertebrates as an example, in comparison with model vertebrates, we will discuss the conservatism of such key processes and mechanisms as: (1) Transport/localization of mRNA by molecular motors; (2) Calcium wave; (3) Transport/localization of molecules by cytoplasmic streaming; (4) Segregation of determinant molecules by PAR protein networks; (5) Segregation of determinant molecules by actin filaments and myosins. The most general problem in this area is how cytoskeletal structures and protein networks are organized and reorganized, and how they interact with calcium waves, cytoplasmic streaming, and active transport by molecular motors. It is important that these conserved processes interact with each other, and the modes and mechanisms of their interaction also tend to be conservative. Thus, the transport of developmental determinants by motors along the cytoskeleton is interconnected with virtually all other processes. It is also significant that these processes and mechanisms also tend to form conservative scenarios. Thus, the prototypical scenario calcium wave → reorganization of actin-myosin cytoskeleton → generation of cytoplasmic flows can be traced back to mammals and humans, and is easier to study in detail in models. Finally, many of the conserved components under consideration turn out to be involved in pathological processes, including oncology. Thus, genes and the factors of the PAR network encoded by them, key to the mechanisms of cellular polarization, are characterized as oncogenes/oncofactors for a number of model objects. Analysis of large-scale studies of the processes and mechanisms of early development of model organisms raises a number of general evolutionary questions, discussed in the conclusion of this review.