Fig. 2. Expression of Xema during early development. (A) RT-PCR analysis of Xema temporal expression. The `-RT' lane contains all reagents except for reverse transcriptase and was used as a negative control. Ornithine decarboxylase (ODC) was used as a loading control (Bassez et al., 1990). Chordin expression is initiated zygotically and was used as a staging control. (B) Whole-mount in situ hybridization of early gastrula (stage 10+), midgastrula (stage 11), and early neurula (stage 15) stage embryos, using antisense Xema and Xenopus brachyury (Xbra) probes. Xema expression is seen as a blue stain throughout the animal pole of gastrula-stage albino embryos; Xema expression is excluded from the marginal zone (denoted by arrows at stage 11) and vegetal pole. Expression of the panmesodermal marker Xbra is found only in the marginal zone of gastrula stage embryos and was used as a control. Xema is expressed in the vental ectoderm (epidermis) of early neurula stage embryos (ventral view); expression is excluded from the neural plate (dorsal view). (C) RT-PCR analysis of Xema expression in early gastrula stage explants. EF1- was used as a loading control (Krieg et al., 1989). Xbra is a panmesodermal marker at this stage (Smith et al., 1991), chordin is a dorsal endomesodermal marker (Sasai et al., 1994), and Xwnt8 is a ventrolateral marker (Christian et al., 1991; Smith and Harland, 1991).