Identification and expression analysis of two novel members of the Mesp family in zebrafish

Abstract

Mesp proteins play crucial roles in the formation of heart, vasculature and somites during vertebrate embryogenesis. We have used phylogenetic and genomic analysis, combined with qRT-PCR and in situ hybridization, to characterize two novel additional mesp genes in zebrafish, mesp-ab and mesp-bb, and describe their expression pattern in wild type and segmentation mutants. Both mesp-ab and mesp-bb are expressed in early mesoderm with mesp-ab expression starting during late blastula stages and mesp-bb expression initiating later, at the end of gastrulation. During somitogenesis, both mesp genes are expressed dynamically in the anterior presomitic mesoderm. mesp-ab is expressed in presumptive somites S-I and S-II, while mesp-bb is detected in S-I, S-II and S0, with expression restricted to the rostral compartment of presumptive somites. We show that the segmentation clock program regulates expression of these newly identified zebrafish mesp genes in a similar manner to their ohnologs, mesp-aa and mesp-ba. We also present evidence that zebrafish, minnow and salmon retained these additional mesp genes after the teleost whole genome duplication, while medaka, stickleback, fugu and tetraodon did not. Finally we show that although expression and regulation of zebrafish mesp genes appears highly comparable, there is no conservation in non-coding regions with other teleosts. In this study we have completed the description of the Mesp family in zebrafish, which will enable correct genome annotation and facilitate further functional studies on the role of these proteins in zebrafish.

Tbx6, Mesp-b and Ripply1 regulate the onset of skeletal myogenesis in zebrafish

“…Our data suggest that Tbx6 directly regulates the expression of both mesp-b paralogs in vivo (see also Kawamura et al, 2008;Cutty et al, 2012). Binding of Tbx6 to the mesp-b promoter and the functional relevance of this interaction have been demonstrated in other vertebrate models, including medaka (Terasaki et al, 2006), Xenopus (Tazumi et al, 2008) and mouse (Yasuhiko et al, , 2008, suggesting that this interaction is conserved.…”

“…We identified regions of Tbx6 binding in close proximity to the mesp-ba, mesp-bb and ripply1 genes ( Fig. 1F; supplementary material Table S1), many of which match those found computationally using the T-box consensus motif (Cutty et al, 2012). De novo motif discovery showed that the Tbx6…”

“…The rapid changes in mRNA levels occurred similarly in all somites, independent of their maturation state, and did not affect the Shown are 35-kb windows encompassing significant peaks in reads per million (RPM) (supplementary material Table S1). Black asterisks indicate correspondence with T-box binding sites identified by Cutty et al (2012). Red asterisks indicate peaks confirmed by ChIP-PCR (supplementary material Fig.…”

Conserved non-coding elements and cis regulation: actions speak louder than words

“…2), but that have conserved expression, regulation and function during vertebrate development (e.g. Cutty et al, 2012). As discussed further below, it has also been shown that functional regulatory elements are very flexible and the same gene expression outcome can be brought about by a non-conserved sequence.…”

Quadruple zebrafish mutant reveals different roles of Mesp genes in somite segmentation between mouse and zebrafish

“…The zebrafish has four Mesp genes, mespaa, mespab, mespba and mespbb, all of which are expressed in the anterior PSM during somitogenesis (Sawada et al, 2000;Durbin et al, 2000;Cutty et al, 2012). However, the roles of these Mesp genes in somitogenesis remain unclear.…”