Fig. 1

Fig. 1 Early expression of pitx2 transcripts during Xenopus development. (A) Deduced N-terminal sequences of three Pitx2 isoforms. The sequence common to the different Pitx2 isoforms is in green. The junction between the variable and the common regions coincides with the beginning of exon 5 in pitx2 (see Schweickert et al., 2000, for the genomic organization of the pitx2 locus). (B) Northern blot of total RNA prepared at the indicated stages. The blot was probed with an antisense RNA probe derived from the 3′ UTR of the cDNA. Similar results were obtained with a probe containing the coding region. (C) RT-PCR analysis showing that in Xenopus, pitx2b, and pitx2d are expressed maternally and zygotically while pitx2c is expressed only after MBT. RT-PCR was performed with total RNA prepared at the indicated stages. (D) Expression of pitx2 in early Xenopus gastrulae (st 10^1/2) analyzed by dissection and RT-PCR. pitx2b and pitx2c are expressed predominantly in the vegetal and marginal regions while pitx2d is expressed uniformly. Material from a single embryo was used for the 1RT control. Five embryos were used for the animal, vegetal, and equatorial explants and two for the dorsal and ventral fragments. (E–H) pitx2 in situ hybridizations showing an early broad expression at the blastula stage and expression in the dorsal mesoderm and endoderm at the gastrula stage. In situ hybridizations of bisected embryos are shown in E and G and of whole embryos in F and H. (E) Side view showing ubiquitous expression of pitx2 at the late blastula stage (stage 9^3/4). Note the punctate staining in the vegetal hemisphere. (F) Midgastrula (stage 11) vegetal view, dorsal side at top. (G) Lateral view, dorsal side on the right. pitx2 transcripts are transiently enriched in the involuting dorsal mesoderm. A slight dorsal–ventral gradient of pitx2 transcripts is apparent in the ectoderm, mesoderm, and, to a lesser extent, endoderm. (H) Cleared neurula (stage 15). The most prominent expression of pitx2 is in the anterior ectoderm and prechordal mesoderm.