Novel gene expression domains reveal early patterning of the Xenopus endoderm

R.M.B. Costa, J. Mason, M. Lee, E. Amaya and A.M. Zorn

Gene Expression Patterns 3:509-519 (2003) (Full Article, 1900K).

ABSTRACT

The endoderm gives rise the respiratory and digestive tract epithelia as well as associated organs such as the liver, lungs

and pancreas. Investigations examining the molecular basis of embryonic endodermal patterning and organogenesis

have been hampered by the lack of regionally expressed molecular markers in the early endoderm. By differentially

screening an arrayed cDNA library, combined with an in situ hybridization screen we identified 13 new genes

regionally expressed in the early tailbud endoderm of the Xenopus embryo. The putative proteins encoded by these

cDNAs include a cell surface transporter, secreted proteins, a protease, a protease inhibitor, an RNA-binding protein, a

phosphatase inhibitor and several enzymes. We find that the expression of these genes falls into one of three re-

occurring domains in the tailbud embryo; 1) a ventral midgut, 2) posterior to the midgut and 3) in the dorsal endoderm

beneath the notochord. Several of these genes are also regionally expressed at gastrula and neurula stages and appear to

mark territories that were previously only predicted by the endodermal fate map. This indicates that there is significant

positional identity in the early endoderm long before stages 28-32 when regional specification of the endoderm is

thought to occur. These new genes provide valuable tools for studying endodermal patterning and organogenesis in

Xenopus.

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