A functional Bucky ball-GFP transgene visualizes germ plasm in living zebrafish.

In many animals, the germline is specified by maternal RNA-granules termed germ plasm. The correct localization of germ plasm during embryogenesis is therefore crucial for the specification of germ cells. In zebrafish, we previously identified Bucky ball (Buc) as a key regulator of germ plasm formation. Here, we used a Buc antibody to describe its continuous germ plasm localization. Moreover, we generated a transgenic Buc-GFP line for live imaging, which visualizes germ plasm from its assembly during oogenesis up to the larval stages. Live imaging of Buc-GFP generated stunning movies, as they highlighted the dynamic details of germ plasm movements. Moreover, we discovered that Buc was still detected in primordial germ cells 2 days after fertilization. Interestingly, the transgene rescued buc mutants demonstrating genetically that the Buc-GFP fusion protein is functional. These results show that Buc-GFP exerts all biochemical interactions essential for germline development and highlight the potential of this line to analyze the molecular regulation of germ plasm formation.