Ripply3, a Tbx1 repressor, is required for development of the pharyngeal apparatus and its derivatives in mice

Abstract

SUMMARYThe pharyngeal apparatus is a transient structure that gives rise to the thymus and the parathyroid glands and also contributes to the development of arteries and the cardiac outflow tract. A typical developmental disorder of the pharyngeal apparatus is the 22q11 deletion syndrome (22q11DS), for which Tbx1 is responsible. Here, we show that Ripply3 can modulate Tbx1 activity and plays a role in the development of the pharyngeal apparatus. Ripply3 expression is observed in the pharyngeal ectoderm and endoderm and overlaps with strong expression of Tbx1 in the caudal pharyngeal endoderm. Ripply3 suppresses transcriptional activation by Tbx1 in luciferase assays in vitro. Ripply3-deficient mice exhibit abnormal development of pharyngeal derivatives, including ectopic formation of the thymus and the parathyroid gland, as well as cardiovascular malformation. Corresponding with these defects, Ripply3-deficient embryos show hypotrophy of the caudal pharyngeal apparatus. Ripply3 represses Tbx1-induced expression of Pax9 in luciferase assays in vitro, and Ripply3-deficient embryos exhibit upregulated Pax9 expression. Together, our results show that Ripply3 plays a role in pharyngeal development, probably by regulating Tbx1 activity.

Reiterative expression of pax1 directs pharyngeal pouch segmentation in medaka (Oryzias latipes)

“…Accompanying such functional transition, alternative factors might have been recruited to the pouch segmentation regulatory network. Ripply3, which encodes a repressor of Tbx1, is a conceivable candidate, as this gene is expressed in the mouse pharyngeal endoderm in a similar fashion to medaka pax1, and its function is necessary for the segmentation of the third and posterior pouches (Okubo et al, 2011). Interestingly, the pouch defects that we found in pax1 mutant medaka are almost identical to those seen in Ripply3 mutant mice.…”

“…Tbx1 is expressed in the pharyngeal ectoderm, endoderm and mesoderm (Chapman et al, 1996;Vitelli et al, 2002;Piotrowski et al, 2003). In mice, although mesodermal Tbx1 is required for proper pouch development (Zhang et al, 2006), dynamic expression of Ripply3, which encodes a Tbx1 repressor, regulates the endodermal activity of Tbx1 to form pouches posterior to the second arch (Okubo et al, 2011). In zebrafish, mesodermal tbx1 drives endodermal pouch morphogenesis by upregulating the expression of wnt11r and fgf8 in a cell-autonomous manner (Choe and Crump, 2014).…”

RIPPLY3 is a retinoic acid-inducible repressor required for setting the borders of the pre-placodal ectoderm

“…Xenopus Ripply3 is orthologous to human DSCR6 and belongs to the Ripply/Bowline gene family. Ripply3 is primarily associated with the development of the thymus, parathyroid and thyroid gland in mice (Okubo et al, 2011) but it is notable that Down Syndrome is associated with defects in sensory organs. We demonstrate a novel role for RIPPLY3 in regulating the boundaries of the PPE, with TBX1 being an integral player in this process, downstream of RA signaling.…”

“…Recently, it was shown in Cos7 cells that TBX1 could repress reporter gene activity in the presence of RIPPLY3 (and that repression was dependent on the WRPW domain), whereas TBX1 would activate reporter gene activity in the absence of RIPPLY3 (Okubo et al, 2011). We tested the effects of Ripply3 on the ability of Tbx1 to activate reporter gene constructs in vivo, and whether the effects required the interaction of RIPPLY3 with GROUCHO and TBX1.…”

“…RIPPLY3 sets the posterolateral boundary of the PPE Although much is known about Tbx1, Ripply3 has primarily been studied in the pharyngeal apparatus, and in heart development (Okubo et al, 2011). Zebrafish Ripply1 (Kawamura et al, 2005), mouse Ripply2 (Biris et al, 2007;Chan et al, 2007) and Xenopus Bowline/Ledgerline (Ripply2) (Chan et al, 2006;Kondow et al, 2006) participate in setting somite boundaries during somitogenesis.…”