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The prickle-related gene in vertebrates is essential for gastrulation cell movements.
Takeuchi M
,
Nakabayashi J
,
Sakaguchi T
,
Yamamoto TS
,
Takahashi H
,
Takeda H
,
Ueno N
.
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Involving dynamic and coordinated cell movements that cause drastic changes in embryo shape, gastrulation is one of the most important processes of early development. Gastrulation proceeds by various types of cell movements, including convergence and extension, during which polarized axial mesodermal cells intercalate in radial and mediolateral directions and thus elongate the dorsal marginal zone along the anterior-posterior axis [1,2]. Recently, it was reported that a noncanonical Wnt signaling pathway, which is known to regulate planar cell polarity (PCP) in Drosophila [3,4], participates in the regulation of convergent extension movements in Xenopus as well as in the zebrafish embryo [5-8]. The Wnt5a/Wnt11 signal is mediated by members of the seven-pass transmembrane receptor Frizzled (Fz) and the signal transducer Dishevelled (Dsh) through the Dsh domains that are required for the PCP signal [6-8]. It has also been shown that the relocalization of Dsh to the cell membrane is required for convergent extension movements in Xenopus gastrulae. Although it appears that signaling via these components leads to the activation of JNK [9,10] and rearrangement of microtubules, the precise interplay among these intercellular components is largely unknown. In this study, we show that Xenopus prickle (Xpk), a Xenopus homolog of a Drosophila PCP gene [11-13], is an essential component for gastrulation cell movement. Both gain-of-function and loss-of-function of Xpk severely perturbed gastrulation and caused spina bifida embryos without affecting mesodermal differentiation. We also demonstrate that XPK binds to Xenopus Dsh as well as to JNK. This suggests that XPK plays a pivotal role in connecting Dsh function to JNK activation.
Figure 1. Xpk and Zpk Antisense Morpholino Oligos (MO) Inhibit Convergent Extension Movements(A) Whole-mount in situ hybridization of Xpk in staged embryos; early gastrula stage 10.5 (a and b, vegetal and lateral views, respectively), late gastrula stage 13 (c and d, vegetal and dorsal views, respectively), and early neurula stage 15 (e and f, posterior and dorsal views, respectively). In (a), (c), and (e), the dorsal side is at the top. In (b), the dorsal side is at the right.(B) Northern blot analysis of Xpk. The numbers at the top of each lane indicate developmental stages. Two Xpk transcripts of around 5 kb are detected in eggs to stage 32 embryos. ODC is the RNA loading quantity control.(C) Animal cap assay; Xpk expression is induced in animal cap cells in a dose-dependent manner by the overexpression of Xbra.(D) mo-Xpk injection perturbs the correct gastrulation movements and activin-induced elongation of animal cap explants. (a) Uninjected sibling embryo at the tadpole stage (left panel) and 0.5 pg activin mRNA-injected animal cap explants (right panel). (b) Unrelated mo has no effect when injected dorsally (left panel) or in the animal cap elongation assay (right panel). (c) 4mis mo-Xpk has little effect when injected dorsally (left panel) or in the animal cap elongation assay (right panel). (d) mo-Xpk 10-pmol dorsally injected embryo (left panel) and animal cap coinjected with activin and mo-Xpk (left panel).(E) mo-Xpk prevented the translation of overexpressed Xpk-GFP, but unrelated mo or 4mis mo-Xpk had no or little effects, respectively. Translation of coinjected GFP mRNA as a negative control was not prevented.(F) In the animal cap elongation assay, mo-Xpk does not interfere with mesoderm induction (Xbra expression) or expression of either Xwnt11 or Xpk itself. Histone H4 is the cDNA loading quantity control.(G) Zpk knockdown with mo-Zpk inhibits dorsal convergence. Phenotypes are observed at the10 somite stage, 17 hpf ([a and b], lateral view; [c–f], dorsal view; [g and h], anterior view) and prim-20 stage, 33 hpf (i–k). (a, c, e, g, and i), uninjected controls. (b, d, f, h, and j), mo-Zpk 0.5 pmol-injected phenotypes. These phenotypes were similar to mo-Zpk version 2 that recognizes the distinctive site of Zpk 5′-UTR (our unpublished data). (k) 4mis mo-Zpk-injected phenotype. (e,f) Whole-mount in situ hybridization of myoD (red).
Figure 2.
Structure-Function Relationship of XPK: Overexpression of Wild-Type and XPK Deletion Constructs
(A) Structures of wild-type XPK and deletion constructs; ÎPET, ÎLIM, ÎP/L, and P/L are illustrated in (a). (b) All of these constructs inhibit activin-induced elongation of animal cap explants (wild-type and ÎPET, 500 pg; ÎLIM, 1 ng; ÎP/L and P/L, 250 pg). (c) None of the XPK constructs affect activin-induced Xbra and Xwnt11 expression in animal cap explants at stage 10.5. The indicated numbers correspond to (b1â6).
(B) All of the constructs perturb normal gastrulation movements when injected into the dorsal embryo. Phenotypes of abnormal gastrulation were classified into three grades that indicated (a) (1) a normal or weak phenotype showing a small head but nearly normal-sized trunk and tail, (2) an intermediate phenotype showing a short and curved body axis, or (3) a severe, spina bifida-like phenotype showing an open blastopore. (b) Effects of LIM domain-deleted Xpk injection are rescued by the coinjection of wild-type Xpk mRNA. In this bar graph, the phenotypes caused by injection of these constructs into the dorsal embryo were scored as 1, 2, or 3 and are indicated with white, gray, and black color, respectively. (c) An example of phenotype rescue. The result of injecting ÎP/L at 250 pg is shown in the upper panel, and the phenotype resulting from injecting ÎP/L with wild-type Xpk at 500 pg is shown in the lower panel. The ratio of abnormal embryos was reduced by the coexpression of wild-type Xpk.
Figure 3.
XPK Interacts Physically with Dishevelled and JNK to Activate JNK in HEK293T Cells
(A) JNK activation could not be detected in Xpk-transfected cells, but Xdsh alone could activate JNK in a dose-dependent manner.
(B and C) Two-phase XPK activity, depending on the Xdsh dose. (B) At a low Xdsh dose, wild-type XPK enhances Xdsh-mediated JNK activation. (C) At a high Xdsh dose, wild-type XPK or ÎP/L suppresses the activation of JNK, which is mediated by Xdsh. HEK293T cells were transfected with the indicated expression plasmids. The activation of JNK was monitored with an anti-phosphorylated c-Jun antibody. Western blotting with an anti-Gal4DBD antibody was the control for the transfection and loading quantity. (D) XPK interacts physically with Xdsh. (E) Wild-type XPK interacts physically with JNK1.
Figure S1. Intracellular Localization of the XPK Constructs; Neither
XPK nor Its Deletion Mutants Regulate Xdsh Membrane Localization
(A) Intracellular localization of XPK constructs in animal cap cells.
The FLAG-tagged constructs illustrated in the upper panel were
analyzed by confocal microscopy. Wild-type XPK was expressed
ubiquitously, but its expression was slightly greater at the cell membrane
(bottom left). Deletion constructs PET, LIM, and P/L as
well as the C-terminal deletion mutants CEV, Cstu, and CApa
were localized similarly to wild-type XPK, but P/L and CL3 were
found to be localized solely to the nucleus (bottom right).
(B) The localization of the XPK constructs was not altered by the
membrane localization of Myc-Xdsh in response to the Fz7 signal,
and vice versa. The XPK constructs and Xdsh did not interfere with
each otherâs localization.
