Fig. 4. Cooperative action of REPO and TTK69 activates the glial expression of the M84 marker. (A-D) CNS of stage 16 embryos carrying the M84 glial marker. (A) In wild-type embryos, M84 ß-galactosidase expression could be detected in the subperineurial glia and channel glia. (B) In repo mutant embryos, M84 expression was absent or dramatically reduced. (C) pointed mutant embryos expressed the M84 marker at normal levels, although the arrangement of the glial cells was irregular. (D) In ttk mutant embryos, the expression level of M84 was lower than in wild type. (E-H) Ventral views of stage 12 embryos carrying the M84 glial marker. In wild-type embryos, few cells expressed the M84 marker at stage 13 (E). Ectopic expression of REPO induced additional cells to express the M84 marker (F), whereas TTK69 had no effect (G). Co-expression of REPO and TTK69 had a synergistic effect on the activation of the M84 marker (H). (F, inset) Supernumerary M84-positive cells induced by the ectopic expression of REPO also expressed endogenous TTK69. The ectopically expressed M84 marker is shown in magenta and TTK69 is shown in green. An overlay of both colors appears as white. The majority of ectopic M84-positive cells were located in the epidermis, which normally do not express this marker. The number of M84-positive epidermal cells per hemisegment were 10.2±5.8 for REPO misexpression and 32.6±9.7 for co-expression of REPO and TTK69 (n=23). Anterior is leftwards.

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