Zebrafish <i>vasa</i> homologue RNA is localized to the cleavage planes of 2- and 4-cell-stage embryos and is expressed in the primordial germ cells

TLDR

The germ line is crucial for model organism studies, yet zebrafish PGCs have not been previously described despite the species’ recent emergence as a vertebrate development model. The study aimed to identify a molecular marker for zebrafish PGCs by cloning the zebrafish vasa homologue, a germ‑cell‑specific protein in Drosophila. The authors cloned the zebrafish vasa homologue and used whole‑mount in situ hybridization to examine vas RNA expression from the 1‑cell stage through 10 days of development. Northern blotting showed maternally supplied vas transcript, and in situ hybridization revealed vas RNA as a germ‑cell‑specific marker localized to cleavage planes in early embryos, forming subcellular clumps in a few cells that likely become germ cells, providing a basis for future genetic manipulation and studies of germ‑line development.

Abstract

ABSTRACT Identification and manipulation of the germ line are important to the study of model organisms. Although zebrafish has recently emerged as a model for vertebrate development, the primordial germ cells (PGCs) in this organism have not been previously described. To identify a molecular marker for the zebrafish PGCs, we cloned the zebrafish homologue of the Drosophila vasa gene, which, in the fly, encodes a germ-cell-specific protein. Northern blotting revealed that zebrafish vasa homologue (vas) transcript is present in embryos just after fertilization, and hence it is probably maternally supplied. Using wholemount in situ hybridization, we investigated the expression pattern of vas RNA in zebrafish embryos from the 1-cell stage to 10 days of development. Here we present evidence that vas RNA is a germ-cell-specific marker, allowing a description of the zebrafish PGCs for the first time. Furthermore, vas transcript was detected in a novel pattern, localized to the cleavage planes in 2- and 4-cell-stage embryos. During subsequent cleavages, the RNA is segregated as subcellular clumps to a small number of cells that may be the future germ cells. These results suggest new ways in which one might develop techniques for the genetic manipulation of zebrafish. Furthermore, they provide the basis for further studies on this novel RNA localization pattern and on germ-line development in general.