The Xcad-2 gene can provide a ventral signal independent of BMP-4.
Patterning of the marginal zone in the Xenopus embryo has been attributed to interactions between dorsal genes expressed in the organizer and ventral-specific genes. In this antagonistic interplay of activities, BMP-4, a gene that is not expressed in the organizer, provides a strong ventralizing signal. The Xenopus caudal type homeobox gene, Xcad-2, which is expressed around the blastopore with a gap over the dorsal lip, was analyzed as part of the ventral signal. Xcad-2 was shown to efficiently repress during early gastrula stages the dorsal genes gsc, Xnot-2, Otx-2, XFKH1 and Xlim-1, while it positively regulates the ventral genes, Xvent-1 and Xvent-2, with Xpo exhibiting a strong positive response to Xcad-2 overexpression. Xcad-2 was also capable of inducing BMP-4 expression in the organizer region. Support for a ventralizing role for Xcad-2 was obtained from co-injection experiments with the dominant negative BMP receptor which was used to block BMP-4 signaling. Under lack-of-BMP-signaling conditions Xcad-2 could still regulate dorsal and ventral gene expression and restore normal development, suggesting that it can act downstream of BMP-4 signaling or independently of it. Xcad-2 could also inhibit secondary axis formation and dorsalization induced by the dominant negative BMP receptor. Xcad-2 was also shown to efficiently reverse the dorsalizing effects of LiCl. These results place Xcad-2 as part of the ventralizing gene program which acts during early gastrula stages and can execute its ventralizing function in the absence of BMP signaling.
Pillemer
G
G
Department of Cellular Biochemistry, Hebrew University Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel.
Yelin
R
R
Epstein
M
M
Gont
L
L
Frumkin
Y
Y
Yisraeli
J K
JK
Steinbeisser
H
H
Fainsod
A
A
D000818:Animals; D030161:Avian Proteins; D019521:Body Patterning / Q000235:genetics*; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D051858:Forkhead Transcription Factors; D005775:Gastrula / Q000378:metabolism* / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D051956:Goosecoid Protein; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D060850:LIM-Homeodomain Proteins; D008845:Microinjections; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics; D020897:Organizers, Embryonic; D051857:Otx Transcription Factors; D012097:Repressor Proteins; D015398:Signal Transduction; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics; D014157:Transcription Factors; D029867:Xenopus Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics
D030161:Avian Proteins; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D051858:Forkhead Transcription Factors; C000598904:FoxA4 protein, Xenopus; D051956:Goosecoid Protein; D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D060850:LIM-Homeodomain Proteins; C543964:Lhx1 protein, Xenopus; D009419:Nerve Tissue Proteins; C080209:Not protein, Xenopus; D051857:Otx Transcription Factors; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C475218:XPO1 protein, Xenopus; D029867:Xenopus Proteins; C525812:bmp4 protein, Xenopus; C112507:ventx1.2 protein, Xenopus; C099992:ventx2.1 protein, Xenopus