A study of mesoderm patterning through the analysis of the regulation of Xmyf-5 expression.

M. Polli and E. Amaya

Development 129:2917-2927 (2002). Full Article (348K)

Abstract

Xenopus laevis has been a particularly useful model organism for identifying factors involved in the induction and

patterning of the mesoderm, however, much remains to be learned about how these factors interact. The myogenic

transcription factor Xmyf-5 is the earliest known gene to be expressed specifically in the dorso-lateral mesoderm of the

gastrula, a domain that is established by the interaction of dorsal and ventral signals. For this reason, we have begun to

investigate how the expression of Xmyf-5 is regulated. We have identified a 7.28kb Xenopus tropicalis Xmyf-5

(Xtmyf-5) genomic DNA fragment that accurately recapitulates the expression of the endogenous gene. Deletion and

mutational analysis has identified HBX2 an essential element approximately 1.2kb upstream from the start of

transcription, which is necessary for both activation and repression of Xtmyf-5 expression, implying that positional

information is integrated at this site. Electrophoretic mobility shift assays demonstrate that HBX2 specifically interacts

with gastrula stage embryonic extracts and that in vitro translated Xvent-1 proteins binds to one of its functional motifs.

Combined with gain and loss-of-function experiments, the promoter analysis described here suggest that Xvent-1 acts

to repress Xmyf-5 expression in the ventral domain of the marginal zone. Furthermore, the identification of HBX2

provides a tool with which to identify other molecules involved in the regulation of Xmyf-5 expression during

gastrulation.

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