A review of mechanisms of oocyte growth in animal oogenesis

It is a distinctive feature of the egg cell in all animal groups that it is much larger than the somatic cells in the organism it belongs to. This size of the egg cell is due to the accumulation of nutrients called yolk in the cytoplasm during oogenesis. Animals produce their eggs, which reach large volumes in a short time and can be in large numbers, by using some special mechanisms during oogenesis. These mechanisms are grouped as gene amplification, diplotene arrest, the support of extraovarian sources, and the support of accessory cells. Although one or more of these mechanisms are used depending on the species, some mechanisms are common in different animal species. Studies of comparative gametogenesis can be helpful in elucidating and testing hypotheses about the evolution and biogeography of a taxon. Therefore, the investigation of oocyte development in a wider range of species in the animal kingdom by cell and developmental biologists will greatly contribute to our understanding of the underlying mechanisms in this process and the phylogenetic relationships of taxa.