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

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 dorsolateral 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 7.28 kb 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 1.2 kb 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 protein binds to one of its functional motifs. Combined with gain- and loss-of-function experiments, the promoter analysis described here suggests that Xvent-1 functions 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.

Evolution of Somite Compartmentalization: A View From Xenopus

“…The second wave participates in myotome growth ( Gros et al, 2004 and 2005 ). In Xenopus and zebrafish, the first signs of myogenesis appear early, during the blastula/gastrula transition, long before somite formation ( Hopwood et al, 1992 ; Weinberg et al, 1996 ; Coutelle et al, 2001 ; Polli and Amaya, 2002 ). The myogenesis of skeletal muscle is orchestrated in vertebrates by the four bHLH transcription factors of the Myod family ( Comai et al, 2014 ; Hernández-Hernández et al, 2017 ).…”

“…The first wave at the origin of the primitive myotome appears before dermomyotome formation and is composed of two myogenic populations differentiating in different places and times ( Figure 2B ). Indeed, from stage 9.5, Myf5 and Myod1 start to be expressed in the dorso-lateral marginal zone and initiate medial myogenesis, which gives rise to the first differentiated fibers located near the notochord at the gastrulation/neurulation transition ( Gurdon et al, 1984 ; Hopwood et al, 1989 ; Frank and Harland, 1991 ; Hopwood et al, 1991 ; Scales et al, 1991 ; Kato and Gurdon, 1993 ; Fisher et al, 2002 ; Polli and Amaya, 2002 ; Della Gaspera et al, 2012a ). During gastrulation, Myod1 expressed in the marginal zone also participates in the activation of genes involved in somitogenesis and seems to link myogenesis to somite formation ( Maguire et al, 2012 ).…”