A mutation in the zebrafish maternal-effect gene nebel affects furrow formation and vasa RNA localization

Background: In many animals, embryonic patterning depends on a careful inte rplay between cell division and the segregation of localized cellular compo nents. Both of these processes in turn rely on cytoskeletal elements and mo tor proteins. A type of localized cellular component found in most animals is the germ plasm, a specialized region of cytoplasm that specifies the ger m-cell fate. The gene vasa has been shown in Drosophila to encode an essent ial component of the germ plasm and is thought to have a similar function i n other organisms. In the zebrafish embryo, the vasa RNA is localized to th e furrows of the early cellular divisions. Results: We identified the gene nebel in a pilot screen for zebrafish mater nal-effect mutations. Embryos from females homozygous for a mutation in neb el exhibit defects in cell adhesion. Our analysis provides genetic evidence for a function of the microtubule array that normally develops at the furr ow in the deposition of adhesive membrane at the cleavage plane. In additio n, nebel mutant embryos show defects in the early localization of vasa RNA. The vasa RNA localization phenotype could be mimicked with microtubule-inh ibiting drugs, and confocal microscopy suggests an interaction between micr otubules and vasa-RNA-containing aggregates. Conclusions: Our data support two functions for the microtubule reorganizat ion at the furrow, one for the exocytosis of adhesive membrane, and another for the translocation of vasa RNA along the forming furrow. (C) 1999 Elsev ier Science Ltd. Ail rights reserved.