Fig. 4

Northern analysis of the expression of dorsal- and ventral-specific genes at defined developmental time points. Each lane contained RNA harvested from developmentally staged embryos (h, hours of development at 28.5°C). Zygotic gene transcription begins around 3.5 h (Kane and Kimmel, 1993). Transcripts of the panmesodermal gene no tail (2.5-kb transcript) and the organizer-specific gene goosecoid (gsc; predominant transcript 1.4 kb) were first detected at 4.5 h. Although snail1 RNA (1.9-kb transcript) is maternally supplied, a burst of zygotic transcription, corresponding to snail1 gene expression in dorsal mesoderm (Hammerschmidt and Nusslein-Volhard, 1993; Thisse et al., 1993), was detected at 4.5 h. In contrast, transcripts of the ventrally restricted genes eve1 (1.4-kb transcript) and tbx6 (predominant transcript 2.7kb, additional transcript 3.5 kb) were first detected at 5.5 h. eve1, whose domain of expression includes marginal cells of the blastoderm, is maintained in noninvoluting cells of the epiblast. tbx6 is expressed by marginal cells and their involuting derivatives. A photograph of the 18S ribosomal band of the ethidium bromide-stained Northern gel is shown as a loading control.