mta3 acts upstream of scl and lmo2 during primitive hematopoiesis. (A) Injection of 350 pg of mta3 mRNA enhanced expression of the hematopoietic precursor markers scl and lmo2 in posterior lateral mesoderm. All embryos are shown in posterodorsal view. (B) Injection of 375 pg of scl mRNA enhanced gata1 expression in wild-type embryos and rescued gata1 expression in mta3 morphants at the 10-somite stage. Corresponding statistical data are shown on the right. (C) Coinjection of 375 pg of scl and 50 pg of mLmo2 mRNAs enhanced gata1 expression at the 10-somite stage, even if mta3 was knocked down simultaneously. The expression of the paraxial mesoderm marker myod was stained in red. Corresponding statistical data are shown on the right. (D) The majority (32/41) of embryos injected with 300 pg of gata2 mRNA showed normal expression of gata1 and the remaining portion (9/41) of the injected embryos showed slightly reduced expression of gata1. Coinjection of gata2 mRNA with mta3 tMO failed to restore gata1 expression.