Transient nuclear localization of Fyn kinase during development in zebrafish

Fyn protein tyrosine kinase is present in the unfertilized and fertilized e gg, becomes activated within minutes following fertilization, and has been localized to the cortical cytoplasm and spindle apparatus of the zygote. In order to establish the expression pattern of Fyn in the early embryo, we e xamined the distribution pattern of Fyn by immunofluorescence microscopy. F yn protein is distributed evenly among cells of the cleavage stage zebrafis h embryo and is concentrated in the cortical region of each cell. During bl astula and gastrula stages, Fyn was expressed in all cells, however a subpo pulation of cells exhibited strong nuclear staining for Fyn. Nuclear Fyn st aining was not observed after the gastrula period of development, nor in th e adult zebrafish. Immunoprecipitation of Fyn from isolated mid-blastula nu clei confirmed Fyn was present in the nucleus. This is, to our knowledge, t he first demonstration of Fyn kinase, which lacks a nuclear localization si gnal, present in the nucleus. The transient compartmentalization of Fyn in the nucleus could be important in nuclear signaling. Anat Rec 260:115-123, 2000. (C) 2000 Wiley-Liss, Inc.