Cerberus is a head-inducing secreted factor expressed in the anterior endoderm of Spemann's organizer

Xenopus laevis has been instrumental in elucidating a conserved molecular pathway that regulates vertebrate endoderm specification. However, loss-of-function analysis is required to resolve the precise function of the genes involved. For such analysis, antisense oligos and possibly forward genetics are likely to be more effective in the diploid species Xenopus tropicalis than in the pseudotetraploid Xenopus laevis. Here we have isolated most of the tropicalis genes in the endoderm specification pathway, specifically, tVegT, tMixer, tMix, tBix, tGata6, tSox17␣, tSox17␤, tFoxA1, tHex, and tCerberus, which lack the redundant copies that are found in laevis. In situ hybridization analysis has revealed identical expression patterns between the orthologous tropicalis and laevis endoderm genes, thus suggesting conserved genetic functions. Furthermore, we noted that the smaller tropicalis embryos gave better probe penetration than in laevis whole-mount in situ hybridizations-allowing us to visualize transcripts in the deep endoderm in tropicalis, which is difficult in laevis. This study illustrates how an entire genetic pathway can be quickly transferred from laevis to tropicalis due to high sequence conservation between the sister species and the large number of tropicalis-expressed sequence tags that are now available.

Section: Hex and Cerberusmentioning

confidence: 95%

Section: Cdna Library Screeningmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular components of the endoderm specification pathway in Xenopus tropicalis

D'Souza

Lee

Taverner

et al. 2002

“…A secreted molecule named "Cerberus," which is expressed in anterior endoderm, has the property to induce ectopic head structures when microinjected into ventral regions of Xenopus embryos (Bouwmeester et al, 1996;Bouwmeester, 1997). The patterning of the chick forebrain anlage by the prechordal plate has been described by Pera and Kessel (1997).…”

Section: Influence Of Sickle Endoblast On Neurulation and Gastrulationmentioning

confidence: 99%

Origin, fate, and function of the components of the avian germ disc region and early blastoderm: Role of ooplasmic determinants

Callebaut

2005

In the avian oocytal germ disc region, at the end of oogenesis, we discerned four ooplasms (␣, ␤, ␥, ␦) presenting an onion-peel distribution (from peripheral and superficial to central and deep. Their fate was followed during early embryonic development. The most superficial and peripheral ␣ ooplasm plays a fundamental role during cleavage. The ␤ ooplasm, originally localized in the peripheral region of the blastodisc, becomes mainly concentrated in the primitive streak. At the moment of bilateral symmetrization, a spatially oblique, sickle-shaped uptake of ␥ and ␦ ooplasms occurs so that ␥ and ␦ ooplasms become incorporated into the deeper part of the avian blastoderm. These ooplasms seem to contain ooplasmic determinants that initiate either early neurulation or gastrulation events. The early neural plate-inducing structure that forms a deep part of the blastoderm is the ␦ ooplasm-containing endophyll (primary hypoblast). Together with the primordial germ cells, it is derived from the superficial centrocaudal part of the nucleus of Pander, which also contains ␦ ooplasm. The other structure (␥ ooplasm) that is incorporated into the caudolateral deep part of the blastoderm forms Rauber's sickle. It induces gastrulation in the concavity of Rauber's sickle and blood island formation exterior to Rauber's sickle. Rauber's sickle develops by ingrowth of blastodermal cells into the ␥ ooplasm, which surrounds the nucleus of Pander. Rauber's sickle constitutes the primary major organizer of the avian blastoderm and generates only extraembryonic tissues (junctional and sickle endoblast). By imparting positional information, it organizes and dominates the whole blastoderm (controlling gastrulation, neurulation, and coelom and cardiovascular system formation). Fragments of the horns of Rauber's sickle extend far cranially into the lateral quadrants of the unincubated blastoderm, so that often Rauber's sickle material forms three quarters of a circle. This finding explains the regulative capacities of isolated blastoderm parts, with the exception of the anti-sickle region and central blastoderm region, where no Rauber's sickle material is present. In avian blastoderms, there exists a competitive inhibition by Rauber's sickle on the primitive streak and neural plate-inducing effects of sickle endoblast. Avian primordial germ cells contain ␦ ooplasm derived from the superficial part of the nucleus of Pander. Their original deep and central ooplasmic localization has been confirmed by the use of a chicken vasa homologue. We conclude that the unincubated blastoderm consists of three elementary tissues: upper layer mainly containing ␤ ooplasm, endophyll containing ␦ ooplasm, and Rauber's sickle containing ␥ ooplasm). These elementary tissues form before the three classic germ layers have developed.

“…For FGF8, endocytosis regulates the amount of extracellular protein available for signaling, and the distance the protein can travel from the source of production (Scholpp and Brand, 2004). Receptor availability and extracellular antagonists are powerful dynamic regulators of morphogen gradients (Smith and Harland, 1992;Sasai et al, 1994;Bouwmeester et al, 1996;Goodrich et al, 1996;Meno et al, 1996Meno et al, , 1999Thisse and Thisse, 1999;Cheng et al, 2000;Tanegashima et al, 2000;Larrain et al, 2001;Branford and Yost, 2002;Chang et al, 2003;Harms and Chang, 2003;Zhang et al, 2004). In addition, the preferential degradation of a particular mRNA can contribute to formation of a morphogen gradient.…”

Section: Introductionmentioning

confidence: 99%

Xenopus Lefty requires proprotein cleavage but not N‐linked glycosylation to inhibit nodal signaling

Westmoreland

Takahashi

Wright

2007

The Nodal and Nodal-related morphogens are utilized for the specification of distinct cellular identity throughout development by activating discrete target genes in a concentration-dependant manner. Lefty is a principal extracellular antagonist involved in the spatiotemporal regulation of the Nodal morphogen gradient during mesendoderm induction. The Xenopus Lefty proprotein contains a single N-linked glycosylation motif in the mature domain and two potential cleavage sites that would be expected to produce long (Xlefty L ) and short (Xlefty S ) isoforms. Here we demonstrate that both isoforms were secreted from Xenopus oocytes, but that Xlefty L is the only isoform detected when embryonic tissue was analyzed. In mesoderm induction assays, Xlefty L is the functional blocker of Xnr signaling. When secreted from oocytes, vertebrate Lefty molecules were N-linked glycosylated. However, glycan addition was not required to inhibit Xnr signaling and did not influence its movement through the extracellular space. These findings demonstrate that Lefty molecules undergo post-translational modifications and that some of these modifications are required for the Nodal inhibitory function.