Fish PGC cryopreservation: is it a realistic tool for fish conservation biology?

Primordial germ cells (PGCs), are the embryonic cells that will give rise to gametes and could represent a good alternative for conservation of the diploid genome in fish until embryo cryopreservation is achieved. However, two limiting factors should be taken into account before considering PGCs as an ideal cell source for germplasm banking: 1) The existence of a limited number of cells/embryo 2) The necessity of adequate transplantation methods that guarantee genital ridge PGC colonization. Therefore, in order to ensure their contribution to the germline, PGCs must retained their migration capacity after thawing, and in most cases host embryo/larva should be sterilized to avoid endogenous contribution to the germ line. Several cryopreservation and vitrification protocols have been proposed in different species and genetic and epigenetic studies have been performed in order to analyze the effect of freezing/thawing in these cells. Many studies reported promising results confirming PGC genital ridge colonization and even the production of gametes able to produced live fry. Regarding the other limiting factor, the possibility of generating PGCs in vitro from noncommitted embryonic cells represents an extremely useful tool to overcome the limitation of the small PGC number/embryo and has been recently achieved in zebrafish