Germ cells can be lost, rendering an organism unable to reproduce. The predominant line of thought in germline biology tells us that once the germline is lost, it cannot regenerate.
It appears to be the case for most of the canonical model organisms like mice, Xenopus, Drosophila, zebrafish, C. elegans, etc., that germline cannot regenerate. However, in some species, like Playtnereis dumerilii (a marine annelid) and Ciona intestinalis (a marine ascidian), the germline readily regenerates, and appears to do so in a variety of ways, including by converting somatic cells into germline. How does this regeneration happen? What do these cases of germline regeneration tell us about our understanding of the germline and its relationship with soma? Are there conditions under which somatic cells will convert to germline cells? If so, how should we conceive of the relationship between germline and soma? How does germline regeneration differ between and among species?