Analysis of Ripply1/2-deficient mouse embryos reveals a mechanism underlying the rostro-caudal patterning within a somite

Abstract

The rostro-caudal patterning within a somite is periodically established in the presomitic mesoderm (PSM). In the mouse, Mesp2 is required for the rostral property whereas Notch signaling and Ripply2, a Mesp2-induced protein that suppresses Mesp2 transcription, are required for the caudal property. Here, we examined the mechanism behind rostro-caudal patterning by comparing the spatial movement of Notch activity with Mesp2 protein localization in wild-type embryos and those defective in Ripply1 and 2, both of which are expressed in the PSM. Mesp2 protein appears first as a thin band in the middle of the traveling Notch active domain in both wild-type and Ripply1/2-deficient embryos. In wild-type embryos, the Mesp2 band expands anteriorly to the expression front of Tbx6, an activator of Mesp2 transcription. Notch activity becomes localized further anteriorly to this Mesp2 domain, but does not pass over the anterior Mesp2 domain generated in the previous segmentation cycle. As a result, the Notch active domain appears to be restricted between these two Mesp2 domains. In Ripply1/2-deficient embryos, the Mesp2 band becomes more expanded and the Notch domain is finally diminished. Interestingly, Ripply1/2-deficient embryos exhibit anterior expansion of the Tbx6 protein domain, suggesting that Ripply1/2 regulates Mesp2 expression by modulating elimination of Tbx6 proteins. We propose that the rostro-caudal pattern is established by dynamic interaction of Notch activity with two Mesp2 domains, which are defined in successive segmentation cycles by Notch, Tbx6 and Ripply1/2.

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

“…Since Mesp2 regulates the expression of Ripply1 and Ripply2, which subsequently define the anterior edge of the Tbx6 protein domain, in mouse somitogenesis (Takahashi et al, 2010;Morimoto et al, 2007), we next examined the role of Mesp for Ripply gene expression in zebrafish. In the wild-type embryo, ripply1 was expressed at both the anterior PSM and rostral compartment of each somite; whereas ripply2 was expressed in two to three strips in the anterior PSM (Fig.…”

“…In mouse somitogenesis, posterior regression of the Tbx6 domain is severely disrupted in the Mesp2 mutant or Ripply1 and Ripply2 double-mutant embryos. A number of recent studies strongly suggest that Mesp2-dependent generation of anterior border of the Tbx6 protein domain is mediated by Ripply1 and Ripply2 in mouse somitogenesis (Takahashi et al, 2010;Zhao et al, 2015). For instance, expression of Ripply1 and Ripply2 is lost in Mesp2-deficient mouse embryos.…”

“…Mesp2 activates the expression of Ripply1 and Ripply2, which determine the somite boundary position through repression of Tbx6 protein (Oginuma et al, 2008;Takahashi et al, 2010;Zhao et al, 2015). Mesp2 expression is then restricted to the rostral half of predicted somite and activates the expression of Epha4, which is proposed to be involved in morphogenesis of the physical segmental boundary (Nakajima et al, 2006).…”

Copy number analysis of 413 isolated talipes equinovarus patients suggests role for transcriptional regulators of early limb development

“…68,69 We identified a chromosome 6q14.2 microduplication involving RIPPLY2 that incompletely segregates with talipes equinovarus over three generations. Furthermore, the RIPPLY family of proteins have previously been shown to regulate T-box transcription factors during embryogenesis, 70 suggesting a possible link to the PITX1-TBX4 pathway during limb development.…”

The repression of Notch signaling occurs via the destabilization of mastermind-like 1 by Mesp2 and is essential for somitogenesis

“…Previous functional studies have shown that Mesp2 plays valuable roles during somitogenesis via its regulation of several target genes as a transcription factor, including the upregulation of Lfng, Epha4 and Ripply1/2 (Morimoto et al, 2007;Morimoto et al, 2005;Nakajima et al, 2006;Takahashi et al, 2010). Mesp2 has also been shown to have suppressive effects on Notch activity, in part by activating Lfng expression in the rostral somite compartment (Morimoto et al, 2005).…”