The
pictures show the mutually exclusive regions of expression of Xnr3 (blue)
and Xwnt-8 (brown) in the late blastula and early gastrula. Xnr3 was visualized
with a fluorescein probe, an alkaline phosphatase coupled anti-fluorescein
antibody which was developed with NBT/BCIP. The Xwnt-8 was visualized
with a digoxigenin probe, alkaline phosphatase coupled anti-digoxigenin
and vectastain II.
Xnr3 is expressed exclusively in the superficial layer of the organizer (see Smith and Harland, 1995 for more pictures). Note the rapid change from stage 9 to stage 10-. We assume that at these stages the cells expressing Xnr3 are fairly constant (but have not proven this). At later times Xnr3 turns off as cells go around the lip. If the cells expressing Xnr3 are constant at this time, then this region is converging to the dorsal midline.
Xwnt-8 expression changes rapidly when vizualized by this method. At the onset of expression the regions of Xnr3 and Xwnt-8 abut one another, and Xwnt-8 expression is seen throughout the vegetal region (see also Lemaire P; Gurdon JB. A role for cytoplasmic determinants in mesoderm patterning: cell-autonomous activation of the goosecoid and Xwnt-8 genes along the dorsoventral axis of early Xenopus embryos. Development, 1994 May, 120(5):1191-9). As the embryo approaches gastrulation, staining is no longer apparent in the in the region next to the organizer and the vegetal pole. Lateral mesoderm is converging to the dorsal midline at this stage, so the absence of Xwnt-8 staining must reflect extinction of expression, presumably as a result of dorsalizing signals from the organizer. Staining appears punctate because transcripts are most concentrated in the nuclei at these stages.
Xnr3 is expressed exclusively in the superficial layer of the organizer (see Smith and Harland, 1995 for more pictures). Note the rapid change from stage 9 to stage 10-. We assume that at these stages the cells expressing Xnr3 are fairly constant (but have not proven this). At later times Xnr3 turns off as cells go around the lip. If the cells expressing Xnr3 are constant at this time, then this region is converging to the dorsal midline.
Xwnt-8 expression changes rapidly when vizualized by this method. At the onset of expression the regions of Xnr3 and Xwnt-8 abut one another, and Xwnt-8 expression is seen throughout the vegetal region (see also Lemaire P; Gurdon JB. A role for cytoplasmic determinants in mesoderm patterning: cell-autonomous activation of the goosecoid and Xwnt-8 genes along the dorsoventral axis of early Xenopus embryos. Development, 1994 May, 120(5):1191-9). As the embryo approaches gastrulation, staining is no longer apparent in the in the region next to the organizer and the vegetal pole. Lateral mesoderm is converging to the dorsal midline at this stage, so the absence of Xwnt-8 staining must reflect extinction of expression, presumably as a result of dorsalizing signals from the organizer. Staining appears punctate because transcripts are most concentrated in the nuclei at these stages.