The germ plasm is anchored at the cleavage furrows through interaction with 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 the 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 but distinct from Drosophila. We identified non muscle myosin II (NMII) and tight junction (TJ) components such as ZO2 and Claudin-d (Cldn-d) 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 the cleavage furrows where the germ plasm is anchored. In addition, injection of the TJ-receptor Cldn-d produced extra germ plasm aggregates whereas expression of a dominant negative version inhibits germ plasm aggregate formation. Our findings support for the first time a role of TJs in germ plasm localization.