Germ cell-less expression in zebrafish embryos

The gene of germ cell-less (gcl) has been shown to be important in early differentiation of germ cells in Drosophila. Although the gcl homologue genes have been identified in some organisms, there is little data on the expression pattern and functional analysis of the gcl gene in zebrafish. In this research, real-time quantitative reverse transcription-polymerase chain reaction showed that the level of gcl mRNA expression rapidly decreases from the 4-cell stage to the sphere stage at which it reaches a minimum, gradually increases from the 50%-epiboly stage, and then remains stable during the posterior stages. Results of in situ hybridization indicated that the transcripts of zebrafish gcl are evenly distributed in all blastomeres from the 2-cell stage to the blastula period, different from that of vasa, nonas1 and dead end mRNA, and condense into some clusters of cells located along the blastoderm margin from the gastrulation period. During subsequent development, the transcripts are segregated as subcellular clumps to a small number of cells that would migrate to the position of the gonad in the dorsal side. In the adult, gcl mRNA was widely expressed in developing germ cells of both ovary and testis. These data suggest that zebrafish gcl have potentially important roles in the formation of primordial germ cells.