Germ plasm anchors at tight junctions in the early zebrafish embryo

The zebrafish germline is specified during early embryogenesis by inherited maternal RNAs and proteins collectively called germ plasm. Only the cells containing germ plasm will become part of the germline, whereas other cells will commit to somatic cell fates. Therefore, proper localization of germ plasm is key for germ cell specification and its removal is critical for the development of soma. The molecular mechanism underlying this process in vertebrates is largely unknown. Here we show that germ plasm localization in zebrafish is similar to Xenopus and amniotes but distinct from Drosophila. We identified non muscle myosin II (NMII) and tight junction (TJ) components as interaction candidates of Bucky ball (Buc), which is the germ plasm organizer in zebrafish. Remarkably, we also found that TJ protein ZO1 colocalizes with germ plasm and electron microscopy (EM) of zebrafish embryos uncovered TJ like structures at early cleavage furrows. In addition, injection of the TJ-receptor Claudin-d (Cldn-d) produced extra germ plasm aggregates. Our findings discover for the first time a role of TJs in germ plasm localization.