Fig. 2

tar overexpression expands the expression domains of early mesendodermal markers. Embryos were injected with lacZ RNA (200 pg) as a control or with tar RNA (200 pg), fixed during the late blastula period (40% epiboly), and analysed by in situ hybridisation with the marker indicated (upper right). (A, B, lateral view) At this stage, gata5 is normally expressed (A) in four rows of cells at the margin. (B) In tar mRNA-injected embryos, the expression of gata5 is expanded to the fifth and sixth rows. The dotted line indicates the YSL-blastoderm border. (C, D, animal pole view) Similarly, the normal expression of mixer (C) encompasses three to four rows of marginal cells with a patchy appearance. (D) The overexpression of tar leads to an expansion of the mixer expression domain, which appears more uniform. (E, F, animal pole view) The pan-mesodermal marker ntl is expressed in larger domain than gata5 at the margin of control embryo encompassing 8–10 cell diameters (E, not shown). When tar is overexpressed, the ntl expression is expanded to animal pole (F).