B Average number of Prox1a+ve slow fibres in wild type embryos injected with mRNA encoding different forms of mSmo. Prox1 positive cells were quantified in 4 somites in each of 4 embryos for each sample. The error bars indicate SD. Unpaired Student's t-test was used to determine the statistical significance between uninjected embryos and the various Smo mutants (black asterisk); and between mSmoA1 and mSmoA1SA or mSmoA1SD (red asterisk). ***P<0.001; **P<0.01; *P<0.05 and n.s. (not significant). 