Primordial germ cells differentially contribute to the germline in zebrafish

Primordial germ cells (PGCs) are the precursors of the germline and among the first cells to be specified during embryogenesis. Contrary to the common assumption that PGCs directly develop into germline stem cells (GSCs), recent data suggest a more complex picture. To functionally examine PGC contributions to the germline, we developed two Cre-based transgenic systems in zebrafish - Germ traCre and Germbow - which provide inducible and indelible germline lineage tracing. Using these systems and known germline markers, we found that PGCs give rise to at least four distinct clone types which are not spatially restricted along the anterior-posterior axis. Moreover, these differential PGC contributions appear to shape lifelong reproductive potential. Examination of clonal contributions to female gamete production revealed that some PGCs give rise to renewing GSCs and others to transient daughters that contribute an early wave of gametes. Collectively, our findings suggest a revised model of vertebrate germline establishment and differentiation potential, with implications for reproductive potential.