Pregametogenesis: The Earliest Stages of Gonad and Germline Differentiation in Anuran Amphibians.

The gonads of amphibians, like other vertebrates, consist of somatic tissues, which create a specific environment essential for the differentiation of germline cells. The earliest stages of gametogenesis still remain underexplored in anuran amphibians. We propose to introduce the term "pregametogenesis" for a specific period of gonocyte proliferation and differentiation that occurs exclusively during the early stages of gonadal development. This review shows the key steps of early gonad differentiation in anuran amphibians and further compares chromatin reorganization in gonocytes of mammals and hybridogenetic water frogs. In mammals, this phase involves resetting genomic imprinting, which is crucial for determining gene expression in offspring. In hybridogenetic water frogs, we highlight the unique phenomenon of genome elimination, where one parental subgenome is eliminated while the other is replicated. This process, occurring at the same developmental phase as imprinting in mammals, underscores the evolutionary importance of pregametogenesis. The study of amphibian gonocytes provides valuable insights into chromatin reorganization and genome plasticity, offering new perspectives on reproductive biology.