Stern, H.M., Murphey, R.D., Shepard, J.L., Amatruda, J.F., Straub, C., Pfaff, K.L., Weber, G., Tallarico, J.A., King, R.W. and Zon, L.I. (2005) Small molecules that delay S phase suppress a zebrafish bmyb mutant. Nature Chemical Biology. 1(7):366-370.
Bmyb is a ubiquitously expressed transcription factor involved in cellular proliferation and cancer1, 2, 3, 4. Loss of bmyb function in the zebrafish mutant crash&burn (crb) results in decreased cyclin B1 expression, mitotic arrest and genome instability5. These phenotypic observations in crb mutants could be attributed to the decreased expression of cyclin B1, a cell-cycle regulatory protein that is responsible for driving cell progression from G2 through mitosis. To identify small molecules that interact with the bmyb pathway, we developed an embryo-based suppressor screening strategy. In 16 weeks we screened a diverse approx16,000 compound library, and discovered one previously unknown compound, persynthamide (psy, 1), that suppressed bmyb-dependent mitotic defects. Psy- treated embryos showed an S-phase delay, and knockdown of the cell-cycle checkpoint regulator ataxia telangiectasia—and Rad-related kinase (ATR) abrogated the suppression of crb. The DNA synthesis inhibitors aphidicolin (2) and hydroxyurea (3) also suppressed crb. S-phase inhibition upregulated cyclin B1 mRNA, promoting the progression of cells through mitosis. Our study demonstrates that chemical suppressor screening in zebrafish can identify compounds with cell-cycle activity and can be used to identify pathways that interact with specific cell-cycle phenotypes.