Endowed with the task of transmitting the genetic information to the next generation, germ cells are without doubt critical cells for any species that multiplies through sexual reproduction. Recognizing the vital importance of germ cells to species survival, in many lower organisms including Drosophila Melanogaster, Xenopus Laevis and the Zebrafish (Danio Rerio) germ cell formation is rigidly programmed. In these species, germ cell specification occurs through the localization of so-called “germ plasm” to the posterior pole of the unfertilized egg (Baughman and Geijsen, ; Jin and Xie, ; Strome and Lehmann, 2007). Following the first cleavage divisions, cells that receive the germ plasm are destined to become the germline stem cells. Such a pre-determination model of germ cell specification assures that germ cells are set-aside during the earliest steps of embryonic development, protecting them from the lineage specification and differentiation events that craft the body plan of the embryo. In egg-laying species, which have limited control over the embryo's extra-embryonic milieu, the specification of germ cells through pre-localized germ-plasm may protect the germline against environmental influences. The inheritance of germ plasm in lower organisms is sufficient to install a germ cell identity, but the specific mechanisms by which this occurs remain unknown.
Copyright: © 2008 Niels Geijsen and George Q. Daley.