mRNA localization patterns in zebrafish oocytes

In both invertebrate and vertebrate systems, the localization of maternal m RNAs is a common mechanism used to influence developmental processes, inclu ding the establishment of the dorsal/ventral axis, anterior/posterior axis, and the germ line (for review, see Bashirullah et al., 1998. Annu. Rev. Bi ochem. 67, 335-394). While the existence of localized maternal mRNAs has be en reported in the zebrafish, Danio rerio, the precise localization pattern s of these molecules during oogenesis has not been determined. In this stud y, in situ hybridization experiments were performed on zebrafish ovaries an d activated eggs to examine different mRNA localization patterns. The resul ts establish that while some maternal mRNAs remain ubiquitously distributed throughout the oocyte, other mRNAs follow specific localization patterns, including localization to the animal pole, localization to the vegetal pole , and cortical localization. The animal/vegetal axis is first apparent in s tage II oocytes when the earliest mRNA localization is seen. Unique pattern s of localization are seen in mature eggs as well. Some mRNAs maintain thei r oocyte localization patterns, while others localize upon egg activation ( fertilization). (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.