The coding sequences and functions of a number of medically relevant genes are conserved in the spiny dogfish shark and little skate (Cai et al. 2001 (Cai et al. , 2003 Wang et al. 2002; Yang et al. 2002; Mattingly et al. 2004b ). Primary hepatocytes from little skate retain hepatobiliary polarity for at least 8 h and possibly up to several days in culture, offering particular advantages for studies of liverspecific functions . Genomic information applied to existing physiological data in these systems, along with the further development of in vitro cell culture systems, will allow the testing of molecular hypotheses and understanding of regulatory mechanisms that are directly applicable to human biology. Targeted sequencing of well-defined genomic regions generated from BAC clones has been extremely useful in providing supporting genomic information in species for which complete genome data are not available . In addition to constructing four-fold coverage bacterial artificial chromosome libraries from sperm DNA of dogfish shark and little skate (http://www.mdibl.org/research/ skategenome.shtml), an expressed sequence tag (EST) sequencing project is underway to substantially increase the availability of sequence data for these model organisms (Mattingly et al. 2004b ). Over 10,000 sequences are publicly available through the EST database at the National Center for Biotechnology Information (dbEST; Boguski et al. 1993 ) and http://www.mdibl.org/decypher. These data sets are updated as new sequences become available.