Hormone-inducible expression of secreted factors in zebrafish embryos

The study of gene function at later stages of embryonic development by over expression experiments is often complicated by genes exerting different fun ctions at multiple stages of development, which renders analysis of stage-s pecific effects difficult. To address this problem an inducible expression system that supports timed expression of essentially any protein, including secreted proteins was designed. The system is based on a two step mechanis m. A glucocorticoid inducible, Gal4-site binding chimeric transcription fac tor is expressed ubiquitously whereas a gene of interest is placed under th e control of a Gal4-site driven promoter. Treatment of zebrafish embryos in jected with such constructs with the synthetic glucocorticoid dexamethasone results in readily detectable reporter activity within 3 h. The system was tested with induced expression of Xactivin beta B and Xwnt which both were shown to induce morphological abnormalities, as well as alterations in the expression patterns of goosecoid and otx2, respectively. Coinjection of an inducible lacZ reporter vector served as an indicator for expressing cells in embryos. The present results demonstratrate that this is a versatile in ducible expression system for use in vertebrate embryos, that also supports expression of secreted proteins.