Dr. Seymour Kessler

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In the chick embryo, the primitive streak is the first axial structure to develop. The initiation of primitive streak formation in the posterior area pellucida is influenced by the adjacent posterior marginal zone (PMZ). We show here that chick Vg1 (cVg1), a member of the TGFbeta family of signalling molecules whose homolog in Xenopus is implicated in(More)
Mesoderm induction during Xenopus development has been extensively studied, and two members of the transforming growth factor-beta family, activin beta B and Vg1, have emerged as candidates for a natural inducer of dorsal mesoderm. Heretofore, analysis of Vg1 activity has relied on injection of hybrid Vg1 mRNAs, which have not been shown to direct efficient(More)
Within the fertilized egg lies the information necessary to generate a diversity of cell types in the precise pattern of tissues and organs that comprises the vertebrate body. Seminal embryological experiments established the importance of induction, or cell interactions, in the formation of embryonic tissues and provided a foundation for molecular studies.(More)
VegT is an essential maternal regulator of germ layer specification in Xenopus. The localization of VegT mRNA to the vegetal cortex of the oocyte during oogenesis ensures its inheritance by vegetal and not animal cells, and directs the differentiation of vegetal cells into endoderm. Similarly localized mRNAs, Vg1 and Bicaudal-C, are also inherited by(More)
We have analyzed two gene products expressed in the early endoderm of Xenopus laevis: Xlhbox-8, a pancreas-specific transcription factor and intestinal fatty acid binding protein (IFABP), a marker of small intestinal epithelium. Expression of the pancreas marker relies on cell signaling mediated by both the TGF-beta and FGF classes of secreted peptide(More)
Formation of the vertebrate body plan is controlled by discrete head and trunk organizers that establish the anteroposterior pattern of the body axis. The Goosecoid (Gsc) homeodomain protein is expressed in all vertebrate organizers and has been implicated in the activity of Spemann's organizer in Xenopus. The role of Gsc in organizer function was examined(More)
In Xenopus, the prospective endoderm and mesoderm are localized to discrete, adjacent domains at the beginning of gastrulation, and this is made evident by the expression of Sox17 in vegetal blastomeres and Brachyury (Xbra) in marginal blastomeres. Here, we examine the regulation of Sox17alpha expression and the role of Sox17alpha in establishing the(More)
TGFbeta signals play important roles in establishing the body axes and germ layers in the vertebrate embryo. Vg1 is a TGFbeta-related gene that, due to its maternal expression and vegetal localization in Xenopus, has received close examination as a potential regulator of development in Xenopus, zebrafish, and chick. However, a mammalian Vg1 ortholog has not(More)
In this study, we compare the effects of three mRNAs-goosecoid, activin and Xwnt-8- that are able to induce partial or complete secondary axes when injected into Xenopus embryos. Xwnt-8 injection produces complete secondary axes including head structures whereas activin and goosecoid injection produce partial secondary axes at high frequency that lack head(More)
The zebrafish DVR-1 (zDVR-1) gene, like Xenopus Vg1, is present maternally as an unprocessed precursor protein which is distributed ubiquitously along the future dorsoventral axis. Also, like Vg1, overexpression of zDVR-1 in zebrafish directs synthesis of more precursor, but no processed protein. However, the native zDVR-1 precursor is processed to mature(More)