Wnt-Dependent Epithelial Transitions Drive Pharyngeal Pouch Formation

Abstract

SUMMARY The pharyngeal pouches, which form by budding of the foregut endoderm, are essential for segmentation of the vertebrate face. To date, the cellular mechanism and segmental nature of such budding have remained elusive. Here, we find that Wnt11r and Wnt4a from the head mesoderm and ectoderm, respectively, play distinct roles in the segmental formation of pouches in zebrafish. Time-lapse microscopy, combined with mutant and tissue-specific transgenic experiments, reveal requirements of Wnt signaling in two phases of endodermal epithelial transitions. Initially, Wnt11r and Rac1 destabilize the endodermal epithelium to promote the lateral movement of pouch-forming cells. Next, Wnt4a and Cdc42 signaling induce the rearrangement of maturing pouch cells into bilayers through junctional localization of the Alcama immunoglobulin-domain protein, which functions to restabilize adherens junctions. We propose that this dynamic control of epithelial morphology by Wnt signaling may be a common theme for the budding of organ anlagen from the endoderm.

Control of Wnt5b secretion by Wntless modulates chondrogenic cell proliferation through fine-tuning fgf3 expression

“…The presence of maternally deposited Wls in zebrafish eggs, although meaning conditional loss-of-Wls embryos occur naturally, however, makes it technically challenging to generate maternal and zygotic loss-ofWls embryos to evaluate the function of Wls at earlier developmental stages. Functions of Fgf and Wnt signaling in growing embryos have been associated with cell proliferation, differentiation, migration and apoptosis in various developmental processes (Brault et al, 2001;Chi et al, 2003;Choe et al, 2013;Jászai et al, 2003;Rudnicki and Brown, 1997). In this study, we found that Wls modulates proliferation rather than survival of the chondrogenic cells during the development of jaw cartilages because a decrease in proliferation frequency was observed in wls morphants at 48 hpf (Figs 6 and 7).…”

“…In this study, we found that Wls modulates proliferation rather than survival of the chondrogenic cells during the development of jaw cartilages because a decrease in proliferation frequency was observed in wls morphants at 48 hpf (Figs 6 and 7). These results suggest that canonical Wnt, Bmp and Fgf signaling are intact in the Wls-deficient embryos at the stages when cranial NCCs (CNCCs) are forming and migrating out from the neural plate border, because components of these signaling pathways have been shown to play crucial roles in the specification and migration of CNCCs (Choe et al, 2013;Garnett et al, 2012). Another thing worth noticing is that in addition to a prominent jaw defect, obvious brain defects were also present in the 96 hpf wls morphants ( Fig.…”

“…This was not expected because not only has the function of Wls been associated with the secretion of most, if not all, Wnts (Bänziger et al, 2006;Bartscherer et al, 2006;Goodman et al, 2006), but Wnt signaling has also been shown to control the axis development in various vertebrates, including zebrafish, and axis developmental defects have been observed in the Wls-knockout (KO) mice (Fu et al, 2009;Jin et al, 2010;Kelly et al, 1995;Matsui et al, 2005;Ramel et al, 2005;Westfall et al, 2003). Because the observed jaw defects in wls morphants did not represent the combined phenotypes from loss of Wnt4a, Wnt5b, Wnt9a, Wnt11 and Wnt11r (Choe et al, 2013;Curtin et al, 2011;Heisenberg et al, 1996Heisenberg et al, , 2000Rauch et al, 1997), we therefore hypothesized that the presence of maternally inherited Wls might help Wls morphants to bypass the requirement of Wls during early development, or that Wls might not be essentially required for the early stages of zebrafish embryonic development. At later stages, Wls might only control the secretion of a subset of Wnts during the development of jaw cartilages.…”

“…In mice, previous observations have indicated that Wnts can either stimulate chondrogenesis by promoting survival and differentiation of migrating neural crest cells (NCCs), or inhibit chondrogenesis by repressing BMP2-induced chondrocyte gene expression, depending on the developmental stage and the local tissue context (Brault et al, 2001;Liu et al, 2008;Reinhold et al, 2006;Yang et al, 2003). In zebrafish, wnt4a and wnt11r have been shown to regulate the formation of pharyngeal pouches, whereas wnt5b, wnt9a and wnt11 have been shown to regulate the development of pharyngeal arches and chondrocytes (Choe et al, 2013;Curtin et al, 2011;Heisenberg et al, 1996Heisenberg et al, , 2000Kimmel et al, 2001;Rauch et al, 1997). These findings indicate that Wnts mediate distinct effects on the generation and differentiation of chondrocytes.…”

Endoderm convergence controls subduction of the myocardial precursors during heart-tube formation

“…A 5′-entry clone containing a sox17 mini-promoter (Woo et al, 2012) was used to express genes specifically in the endoderm. A 5′-entry clone containing an nkx2.5 promoter (Choe et al, 2013) was used to express genes specifically in myocardial cells. A middle clone encoding mCherry, and a 3′-entry clone encoding the 2A peptide, a zebrafish gna13a-coding region (morpholino-insensitive), and SV40, was created to express Gα 13 a (mCherry is used to identify lines expressing Gα 13 a).…”