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Fig. 7. Distinct activities of ld proteins. (A–H) Lateral views of stage 28 tadpoles, anterior to left. Embryos have been stained for expression of cardiac actin, which is expressed in the heart and somites. (A–D) Injection of 1 ng each of Id2, Id3, and Id4 has no effect on the expression of cardiac actin, suggesting that the mRNAs used in our study are unable to disrupt endogenous myogenic bHLH complexes. (E) Injection of 500 pg of MyoD induces ectopic expression of cardiac actin. (F, H, J, lanes 8 and 10) Id2 and Id4 can block the activities of ectopic MyoD, while Id3 does not do so (G and J, lane 9). Ectopic cardiac actin is marked with red arrowheads. (J) RT-PCR analysis of ectodermal explants injected with Id mRNAs with and without MyoD. mRNA doses are as above. (K) Id4 blocks expression of neural β-tubulin induced by neurogenin (lanes 7–10) and neuroD (lanes 11–14). Neurogenin and neuroD (100 pg each) were injected. Then 1 ng of each Id gene was injected. E, whole embryo control; RT, no reverse transcriptase control; C, uninjected ectoderm control. |
