Fig. 2. MAK causes morphogenetic defects and head abnormalities. Four-cell stage embryos were injected into dorsal equatorial region (A, two injections) or animal pole region (B-D, four injections), with RNAs encoding wild-type MAK, MAK KD or GFP, as indicated, at 2 ng per injection. (A) Morphological analysis of MAK-expressing embryos. Embryos were fixed at stage 38 and scored for axis elongation and head defects. (B) The effect of MAK on morphogenetic movements. Animal caps were isolated from injected midblastula embryos and treated with 50 ng/ml of activin. MAK, but not MAK KD, inhibited animal cap elongation in response to activin. (C) Expression levels of Myc-tagged MAK and MAK-KD, revealed by Western blot analysis with anti-Myc antibodies in lysates of injected embryos at stage 10. (D) MAK does not inhibit mesoderm markers induced in animal caps by activin. Animal cap induction was as in B. The mesodermal markers MyoD, Chordin and Goosecoid were assessed in animal caps by RT-PCR, when sibling embryos reached stage 14. Whole embryo (WE) RNA is a positive control. Uninj., animal caps from uninjected embryos. RT-, no reverse transcriptase. EF-1 is a loading control.