December 1, 1995;
Using a differential screening strategy, we have cloned a novel Xenopus gene, fugacin
, related to the transforming growth factor beta superfamily. Transcripts were detected primarily in the dorsal marginal zone
of late blastula
. Thereafter, they became highly localized to the blastopore lip
of early gastrula
and were not observed at later stages. This gene, which is most homologous to the mouse gene nodal
, displays a new pattern of cysteine residues. These findings highlight the potential role of these growth factors during early vertebrate development.
[+] show captions
FIG. 1. Sequence of Fugacin and comparison with the TGF-b superfamily. (A) The deduced amino acid sequence of the longest fugacin cDNA
clone is shown. A putative signal sequence is underlined and the potential cleavage site is boxed. Cysteines within the mature domain are marked
by asterisks. (B) Structural representation of the TGF-b superfamily members (Kingsley, 1994). (C) Alignment of the seven-cysteine domain in
the TGF-b family. Conserved amino acids are printed on a black background. Residues homologous to those of Fugacin are printed on a gray
background. The five conserved cysteines are marked with asterisks. Gaps introduced to optimize the alignment are represented by dashes.
Cysteines from Fugacin that differ from the family are indicated by arrows. (D) Graphical representation of the sequence relationships between
members of the TGF-b superfamily. The data used for this dendogram have been generated with the Clustal V program. For both the tree and
the amino acid homologies, only sequence of the C-terminal domain was used, starting with the first cysteine from the active domain (see text).
FIG. 2. Whole-mount in situ hybridization with a fugacin antisense riboprobe labeled with digoxigenin. RNA is transiently expressed
in the Spemann organizer. (A) Albino embryo at late blastula (stage 9), vegetal view; dorsal is up. (A1) Dorsal view. Staining is present in
the dorsal mesoderm. (B) At early gastrula (stage 10.25), vegetal view; dorsal is up. (B1) Dorsal view. Staining is restricted to the top of
the blastopore lip. Note that a few vegetal cells are also labeled. (C) Dorsalized LiCl-treated embryo, vegetal view. Staining appears
throughout the marginal zone. (D) Ventralized UV-treated embryo, vegetal view. No staining is visible. (E) Transverse histological section
after whole-mount in situ hybridization at stage 10.25. Staining is restricted to the Spemann organizer.
nodal3.2 (nodal homolog 3, gene 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 10.25, vegetal view, dorsal up.