Nested expression and sequential downregulation of the Xenopus caudal genes along the anterior-posterior axis

Abstract

Expression of the Xenopus Xcad-1 and Xcad-2 genes initiates during early gastrulation exhibiting a dorsoventral asymmetry in their domains of transcription. At mid-gastrulation the ventral preference becomes stronger and the caudal genes take up a posterior localization in their expression, which they will maintain until their downregulation along the dorsal midline. Comparison of the three Xenopus caudal genes revealed a temporal and spatial nested set of expression patterns. The transcription of the caudal genes is sequentially downregulated with the one expressed most caudally (Xcad-2) being shut down first, this sequence is most evident along the dorsal midline. This pattern of expression suggests a role for the caudal genes as posterior determinants along the anteroposterior axis. In chicken, mouse, man and Xenopus three members of the caudal family have been identified in the genome. Even though in Xenopus the Xcad-3 gene has been previously described, in order to obtain a better insight on the role of the caudal genes a comparative study of all three frog genes was performed.

The Wnt signaling mediator tcf1 is required for expression of foxd3 during Xenopus gastrulation

“…1A). To confirm the dorsalized phenotype of the embryos overexpressing tcf1, we analyzed the expression patterns of the dorsal organizer genes chordin (Sasai et al, 1994) and goosecoid (Cho et al, 1991) and of the ventrolateral markers wnt8 (Christian et al, 1991) and cdx1 (Pillemer et al, 1998) by in situ hybridization (Fig. 1B).…”

“…Digoxygenin-labeled antisense probes were synthesized with the Ambion Maxiscript kit and digoxigenin-UTP from Roche. The digoxgeninlabelled antisense RNA probes used were Xenopus chordin (Sasai et al, 1994), Xenopus goosecoid (Cho et al, 1991), Xenopus wnt8 (Christian et al, 1991), Xenopus cdx1 (Pillemer et al, 1998) and Xenopus foxd3 (Dirksen and Jamrich, 1995). All experiments were repeated at least once.…”

“…Many genes expressed on the dorsal side of the embryo were found to be upregulated by overexpression of tcf1, including known direct b-catenin/TCF target genes such as siamois (sia1), xnr3, and dkk1 (Brannon et al, 1997;Chamorro et al, 2005;McKendry et al, 1997). Most of the downregulated genes are known to be expressed in the ventrolateral zone of the embryo, such as cdx1 (Xcad) and wnt8 (Christian et al, 1991;Pillemer et al, 1998). One of the identified upregulated genes was foxd3, which is an essential regulator of dorsal mesoderm development foxd3 expression during mesoderm formation.…”

Negative autoregulation of Oct3/4 through Cdx1 promotes the onset of gastrulation

“…All three Cdx genes are expressed during gastrulation in the involuting cells in either the blastopore, primitive streak, or marginal zone cells depending on the organism (Marom et al, 1997;Pillemer et al, 1998a;Davidson and Zon, 2006;Young and Deschamps, 2009). The marginal zone pattern of Cdx expression in frogs is in agreement with these genes performing a regulatory role related to the process of gastrulation or the early steps in the differentiation of the gastrulating cells.…”

“…The repression of Oct3/4 by Cdx2 suggests that the Cdx factors might be involved in the negative regulation of the pluripotency of ICM and subsequently epiblast cells, thus allowing their differentiation with the onset of gastrulation. During gastrula stages, dynamic Cdx expression in vertebrates localizes mainly to the involuting and differentiating cells populating the primitive streak in chick or mouse or the blastopore lip in Xenopus (Meyer and Gruss, 1993;Marom et al, 1997;Pillemer et al, 1998a). Cdx expression in the involuting cells is also in agreement with a role in the regulation of gastrulation and germ layer formation.…”