Fig. 3. Specification of CGC is maintained in RL cultures independently of Math1 expression. Rhombic lip cells from Math1^+/+ (WT), Math1^ß-gal/+ (Het) and Math1^{ß-gal/ß-gal} (Null) were cultured and analyzed by RT-PCR with Zic1, Zipro1 and ß-actin-specific primers after 3 and 6 days in vitro. The expression of Zic1 and Zipro1 is constant in cultures from all genotypes and along the culturing periods. + and - indicate the presence and absence of reverse transcriptase, respectively.