The role of bruno-like in early zebrafish development

Posttranscriptional gene regulation is important during oocyte maturation and early embryonic development for many species. During these early stages of development, the genome is transcriptionally repressed and changes in gene expression are dependent on differences in the stabilization, localization, and translational regulation of maternal stores of mRNA. One conserved function of the posttranscriptional regulation of maternal transcripts is the establishment of the embryonic axes. In Drosophila, the translational repressor Bruno is required for anterior–posterior, and most likely dorsal–ventral, polarity in the oocyte and embryo through regulation of the maternal transcripts oskar and gurken. In zebrafish there is evidence that supports the existence of a vegetally localized maternal determinant that, shortly after fertilization, is transported to the marginal blastomeres via microtubules and is responsible for the positioning of the organizer and hence the basic body plan. The zebrafish ortholog of Drosophila Bruno is maternally expressed at the vegetal cortex in the early embryo. This localization raises the possibility that bruno-like genes may have a conserved function in axis specification. We have cloned three maternally expressed splice variants of the brul gene and are currently investigating the role of these isoforms in early zebrafish development.