The Zebrafish Glypican Knypek Controls Cell Polarity during Gastrulation Movements of Convergent Extension

Abstract

Mutations in the zebrafish knypek locus impair gastrulation movements of convergent extension that narrow embryonic body and elongate it from head to tail. We demonstrate that knypek regulates cellular movements but not cell fate specification. Convergent extension movement defects in knypek are associated with abnormal cell polarity, as mutant cells fail to elongate and align medio-laterally. Positional cloning reveals that knypek encodes a member of the glypican family of heparan sulfate proteoglycans. Double mutant and overexpression analyses show that Knypek potentiates Wnt11 signaling, mediating convergent extension. These studies provide experimental and genetic evidence that glypican Knypek acts during vertebrate gastrulation as a positive modulator of noncanonical Wnt signaling to establish polarized cell behaviors underlying convergent extension movements.

Initiation of convergence and extension movements of lateral mesoderm during zebrafish gastrulation

“…Under conditions of brief exposure to chemoattractant, cells can respond quickly to turn in any direction (Soll et al, 2002). As has been seen in other teleosts (Trinkaus et al, 1992;Trinkaus, 1998), we find greater meandering in ventral versus lateral mesoderm, which is further from the hypothesized source of dorsal attractant (Myers et al, 2001;Topczewski et al, 2001;Jessen et al, 2002). In contrast, while moving up a gradient of chemoattractant, Dictyostelium form few lateral processes and show reduced turning (VarnumFinney et al, 1987).…”

“…We previously observed that lateral mesodermal cells (80% epiboly, 8.4 hpf) migrated primarily dorsally, frequently with substantial animal or vegetal bias and showed quite variable net dorsal speed (Jessen et al, 2002). Finally, our previous studies in which lateral mesodermal cells labeled at early gastrulation were visualized at early segmentation stages provided another hint of difference in path orientation along the AnVg axis of the mesoderm (Sepich et al, 2000;Topczewski et al, 2001). The labeled cell group moved toward the dorsal midline, forming a broken line along the animal-vegetal (or anterior-posterior) axis.…”

“…To identify genes regulating the initiation of convergence movements of lateral mesodermal cells, we analyzed convergence movements in embryos with defects in two pathways involved in C&E. Embryos in which function of Stat3 was downregulated using antisense morpholino oligonucleotides translation interference (Stat3 MO) had populations of labeled lateral cells show reduced convergence by midgastrulation (Yamashita et al, 2002), while embryos homozygous for trilobite m209 (tri) or knypek m119 (kny) null mutations show reduced convergence at late gastrulation (Sepich et al, 2000;Topczewski et al, 2001;Jessen et al, 2002). We analyzed kny or tri mutants and Stat3-MO-injected embryos to learn when lateral convergence becomes apparent.…”

“…Embryonic morphology has been the primary assay, although study of the cellular bases of these defects have been initiated. For example, Wnt signaling controls cell elongation and orientation (Topczewski et al, 2001;Jessen et al, 2002;Kilian et al, 2003), orientation of cell division planes, (Gong et al, 2004), formation of and stability of cellular protrusions (Wallingford et al, 2000;Ulrich et al, 2003), and speed of cell movement (Topczewski et al, 2001;Jessen et al, 2002;Marlow et al, 2002). Additional pathways that influence C&E movements have been identified.…”

“…Our previous work showed that during early gastrulation, lateral mesoderm cells engage in directed migration to drive C&E movements (Topczewski et al, 2001;Jessen et al, 2002). Between the onset of gastrulation (6 h post fertilization, hpf) and midgastrulation (80% epiboly, 8.4 hpf), lateral mesodermal cell groups converge slowly toward dorsal, while undergoing extension in the animal to vegetal (AnVg) direction.…”