Fig. 6. Regulatory interactions of Six3 and Rx3. Dorsal views of late gastrula (stage 16, A-D), two-somite stage (stage 19, E and F) and six-somite stage embryos (stage 21, G-L). Anterior is towards the left. (A-C) The expression of Six3 (A), Rx3 (B) and Pax6 (C) partially overlap in presumptive forebrain. Anterior end of neural axis indicated by a broken line. (D,E) Overexpression of Six3 results in expanded Rx3 expression (arrowhead) and ectopic expression in the presumptive midbrain (arrow) at early neurula stage (D) and two-somite stage (E). (E) Note expanded expression in enlarged optic vesicle (arrow). (F) Control injected embryo showing wild-type expression. (G-I) Rx3-injected embryos with enlarged optic vesicles (arrowhead) show expanded Six3 (G), Pax6 (H) and Rx2 (I) expression. (J-L) Control injected embryos at same stage. Note that anterior and posterior boundaries of respective expression domains are not shifted in response to Rx3 overexpression (compare G with J,H with K and I with L). Insets in I and L show horizontal sections at comparable level. Note the increased cell number in the Rx3-injected eye (I).