Capsulin is one of the transcription factors Involved in regulating cell differentiation but its biochemical properties and structural characteristics are still unclear In the present study we cloned capsulin from zebrafish which produces large numbers of transparent embryos and has well-characterized developmental stages By alignment the deduced amino acid sequence of zebrafish Capsulin which contains a putative bHLH motif shares very high homology to that of other species with an 72-82% identity Zebrafish Capsulin was also targeted to the nucleus of mammalian cells when overexpressed by transient transfection In order to characterize the structural and biochemical properties of zebrafish Capsulin a recombinant zebrafish Capsulin protein was expressed and purified in Escherichia colt By circular dichroism spectroscopy Capsulin was shown to be 55% alpha-helical The size distribution assay by analytical ultra centrifugation indicated that It existed as a monomer-dimer mixture The results suggested that the recombinant Capsulin has a well-organized and functional structure Finally endogenous Capsulin was distributed mainly in the epicardial cells of zebrafish by immunohistochemistry analysis using antibodies raised against zebrafish Capsulin The present study not only helps us to comparatively analyze capsulin genes across species but it also provides valuable structural information for further studies of Capsulin biological function in the future (C) 2010 Elsevier Inc All rights reserved