Fig. 6

Pax3/7 and Dmbx activation in A11.120. a Two-color fluorescent in situ hybridization for Vsx (green) and Pax3/7 (magenta) showing expression of Pax3/7 anterior and adjacent to Vsx expression, shown in Fig. 4 to correspond to the A11.119 cell. Pax3/7 is thus deduced to be expressed in the sister cell of A11.119, A11.120. This is identical to its expression pattern in Ciona. b Two-color fluorescent in situ hybridization for Vsx (green) and Dmbx (magenta) also showing expression of Dmbx in A11.120 like Pax3/7. This is different from the situation in Ciona, in which Dmbx is detected only later, in the descending decussating neuron (ddN, equivalent to A12.239, the posterior daughter cell of A11.120). c M. occidentalis early tailbud embryo electroporated with Ciona robusta (Cirobu) Fgf8/17/18 reporter plasmids, labeling the A9.30 lineage on one side, with H2B::mCherry-labeled nuclei in magenta and Unc-76::eGFP-labeled cell bodies in green. Inset at right showing higher magnification of boxed area, showing all four descendants of A9.30, arrayed from anterior to posterior. d In situ hybridization of Dmbx coupled to immunostaining of beta-galactosidase (magenta nuclei) driven by Cirobu.Fgf8/17/18>nls::lacZ reporter plasmid, revealing that Dmbx is strongly activated in the A11.120 cell, the mother cell of the ddN. Right panel shows A11.119 entering mitosis indicated by nuclear envelope breakdown and diffusion on nuclearly localized beta-galactosidase (dashed outline). A11.119 appears to divide before the other cells in the MG at this stage, which is also the case in Ciona. This further confirms the precocious activation of Vsx in this cell relative to Ciona (see Fig. 4)