Flow on the right side of the gastrocoel roof plate is dispensable for symmetry breakage in the frog Xenopus laevis

Vick, Philipp; Schweickert, Axel; Weber, Thomas; Eberhardt, Melanie; Mencl, Stine; Shcherbakov, Denis; Beyer, Tina; Blum, Martin

doi:10.1016/j.ydbio.2009.05.547

Cited by 77 publications

(112 citation statements)

References 68 publications

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“…Most crucially, injections of both cells at the two-cell stage do not affect asymmetry, ruling out interference with cilia-driven events at the GRP as the mechanism by which these mutants randomize the LR axis. Because the GRP is strongly affected by reagents injected at four-cell stage (20), our results show that expressing mutant tubulin in GRP cells makes no difference to asymmetry; the key factor that determines whether or not the LR axis will be randomized is whether tubulin mutant mRNA was injected before the two-cell stage and thus was available for translation during the earliest stages of development. The need to function during the first few cleavages (Fig.…”

Section: Discussionmentioning

confidence: 78%

“…S3), allowing us to test spatial requirements for tubulin mutant-induced randomization with respect to the ciliated organ. Targeted injections were made in four-cell stage embryos, in the left-dorsal (LD) blastomere, which is known to be an early precursor of the GRP and the only side required for nodal flow (20), or the right-ventral (RV) cell, whose descendants do not contribute to the GRP (21). Neither injection made at the four-cell stage produced significant levels of heterotaxia (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…S2 and ref. 19); studies of GRP cilia routinely inject at the four-cell stage to target reagents to this structure (20). If tubulins were to function in LR asymmetry at any time after the first few cleavages (e.g., in the GRP during neurulation), injections at the two-or four-cell stages would show the same randomizing effects on asymmetry as do injections at one-cell stage.…”

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confidence: 99%

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Early, nonciliary role for microtubule proteins in left–right patterning is conserved across kingdoms

Lobikin

Wang

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

104

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Many types of embryos' bodyplans exhibit consistently oriented laterality of the heart, viscera, and brain. Errors of left-right patterning present an important class of human birth defects, and considerable controversy exists about the nature and evolutionary conservation of the molecular mechanisms that allow embryos to reliably orient the left-right axis. Here we show that the same mutations in the cytoskeletal protein tubulin that alter asymmetry in plants also affect very early steps of left-right patterning in nematode and frog embryos, as well as chirality of human cells in culture. In the frog embryo, tubulin α and tubulin γ-associated proteins are required for the differential distribution of maternal proteins to the left or right blastomere at the first cell division. Our data reveal a remarkable molecular conservation of mechanisms initiating left-right asymmetry. The origin of laterality is cytoplasmic, ancient, and highly conserved across kingdoms, a fundamental feature of the cytoskeleton that underlies chirality in cells and multicellular organisms.C. elegans | Xenopus | symmetry breaking C onsistent laterality is a fascinating aspect of embryonic development and has considerable implications for the physiology and behavior of the organism. Although vertebrates are generally bilaterally symmetric externally, most internal organs, such as the heart, viscera, and brain display asymmetric structure and/or unilateral positioning with respect to the left-right (LR) axis. A common defect in LR patterning is the loss of concordance among the sidedness of individual organs known as heterotaxia. In human beings, abnormalities in the proper development of laterality occur in more than 1 in 8,000 live births and often have significant medical consequences (1). Organ asymmetry is highly conserved among species; however, considerable controversy exists about the early steps of LR patterning among phyla (2-4) and the physical mechanisms that can break symmetry (5).One model predicts that cilia-driven extracellular fluid flow during gastrulation is the origin of LR asymmetry (6). Because numerous species initiate asymmetry before (or without) the presence of cilia (7,8), this model implies that asymmetry generation must be poorly conserved, with numerous distinct mechanisms used throughout phyla. However, "ciliary" proteins, such as left-right dynein, known to be important for LR patterning, also have intracellular roles compatible with cilia-independent functions in laterality (9-12). In contrast to the nodal flow model, we have suggested that asymmetry is instead an ancient, well-conserved property of individual cells arising from the chirality of cytoskeletal structures that is subsequently amplified by physiological mechanisms (4,12,13). Thus, we sought the most evolutionarily distant model systems, and ones that are known not to rely on cilia for LR patterning, to test the hypothesis of fundamental molecular conservation of asymmetry mechanisms.Recent findings in Arabidopsis thaliana have shown that mutatio...

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Section: Discussionmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Early, nonciliary role for microtubule proteins in left–right patterning is conserved across kingdoms

Lobikin

Wang

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

104

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“…To monitor the hovering movement of embryos, we anaesthetized embryos with MS-222 (Sigma) on agar plates. First, the embryo was placed on the uninjected left side, and then, it was flipped to the injected right side as described in a previous study 46 . To assess the fluid flow, we immobilized anaesthetized embryos at stage 33/34 in 1% Steinberg agar plates and added fluorescent beads (F8844, Invitrogen) to the culture media.…”

Section: Methodsmentioning

confidence: 99%

ERK7 regulates ciliogenesis by phosphorylating the actin regulator CapZIP in cooperation with Dishevelled

et al. 2015

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Cilia are essential for embryogenesis and maintenance of homeostasis, but little is known about the signalling pathways that regulate ciliogenesis. Here, we identify ERK7, an atypical mitogen-activated protein kinase, as a key regulator of ciliogenesis. ERK7 is strongly expressed in ciliated tissues of Xenopus embryos. ERK7 knockdown markedly diminishes both the number and the length of cilia in multiciliated cells, and it inhibits the apical migration of basal bodies. Moreover, ERK7 knockdown results in a loss of the apical actin meshwork, which is required for the proper migration of basal bodies. We find that the actin regulator CapZIP, which has been shown to regulate ciliogenesis in a phosphorylation-dependent manner, is an ERK7 substrate, and that Dishevelled, which has also been shown to regulate ciliogenesis, facilitates ERK7 phosphorylation of CapZIP through binding to both ERK7 and CapZIP. Collectively, these results identify an ERK7/Dishevelled/CapZIP axis that regulates ciliogenesis.

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“…I have also asked, is there any effect of animal model on the penetrance of LR defects? Importantly, when collecting this data, it was also apparent that many studies examine only asymmetric gene expression and use this data to make conclusions about organ position [see for example (Oki et al, 2010; Antic et al, 2010; Vick et al, 2009; Pathak et al, 2007; Houde et al, 2006; Kramer-Zucker et al, 2005; Zhang et al, 2001)]. A few studies have proposed that gene expression can be used to predict organ laterality, but the mathematical models produced to date have only been applied to extremely limited datasets (Ibanes and Izpisua Belmonte, 2009; Lohr et al, 1997; Mogi et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Laterality defects are influenced by timing of treatments and animal model

Vandenberg

2012

Differentiation

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The timing of when the embryonic left-right (LR) axis is first established and the mechanisms driving this process are subjects of strong debate. While groups have focused on the role of cilia in establishing the LR axis during gastrula and neurula stages, many animals appear to orient the LR axis prior to the appearance of, or without the benefit of, motile cilia. Because of the large amount of data available in the published literature and the similarities in the type of data collected across labs, I have examined relationships between the studies that do and do not implicate cilia, the choice of animal model, the kinds of LR patterning defects observed, and the penetrance of LR phenotypes. I found that treatments affecting cilia structure and motility had a higher penetrance for both altered gene expression and improper organ placement compared to treatments that affect processes in early cleavage stage embryos. I also found differences in penetrance that could be attributed to the animal models used; the mouse is highly prone to LR randomization. Additionally, the data were examined to address whether gene expression can be used to predict randomized organ placement. Using regression analysis, gene expression was found to be predictive of organ placement in frogs, but much less so in the other animals examined. Together, these results challenge previous ideas about the conservation of LR mechanisms, with the mouse model being significantly different from fish, frogs and chick in almost every aspect examined. Additionally, this analysis indicates that there may be missing pieces in the molecular pathways that dictate how genetic information becomes organ positional information in vertebrates; these gaps will be important for future studies to identify, as LR asymmetry is not only a fundamentally fascinating aspect of development but also of considerable biomedical importance.

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Flow on the right side of the gastrocoel roof plate is dispensable for symmetry breakage in the frog Xenopus laevis

Cited by 77 publications

References 68 publications

Early, nonciliary role for microtubule proteins in left–right patterning is conserved across kingdoms

Early, nonciliary role for microtubule proteins in left–right patterning is conserved across kingdoms

ERK7 regulates ciliogenesis by phosphorylating the actin regulator CapZIP in cooperation with Dishevelled

Laterality defects are influenced by timing of treatments and animal model

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