Cilia are cell surface organelles found on most epithelia in vertebrates. Specialized groups of cilia play critical roles in embryonic development, including left-right (LR) axis formation. Recently, cilia have been implicated as recipients of cell-cell signaling1, 2. However, little is known about cell-cell signaling pathways that control the length of cilia3. Here we provide several lines of evidence showing that fibroblast growth factor (FGF) signaling regulates cilia length and function in diverse epithelia during zebrafish and Xenopus development. Morpholino (MO) knockdown of FGF receptor 1 (FGFR1) in zebrafish cell-autonomously reduces cilia length in Kupffer’s vesicle (KV) and perturbs directional fluid flow required for LR patterning of the embryo. Expression of a dominant-negative FGFR (DN-FGFR), treatment with SU5402, a pharmacological inhibitor of FGF signaling, or genetic and morpholino reduction of redundant FGF ligands FGF8 and FGF24, reproduces this cilia length phenotype. Knockdown of FGFR1 also results in shorter tethering cilia in the otic vesicle and shorter motile cilia in the pronephric ducts. In Xenopus, expression of a DN-FGFR results in shorter monocilia in the gastrocoel roof plate (GRP) that control LR patterning4 and in shorter multicilia in external mucociliary epithelium. Together, these results suggest a fundamental and highly conserved role for FGF signaling in the regulation of cilia length in multiple tissues. Abrogation of FGFR1 signaling down-regulates expression of two ciliogenic transcription factors, foxj1 and rfx2, and the intraflagellar transport (IFT) gene, polaris, suggesting that FGF signaling mediates cilia length through an FGF8/FGF24 - FGFR1- IFT pathway. We propose that a subset of developmental defects and diseases ascribed to FGF signaling are due in part to loss of cilia function.

gamma-Glutamyl transpeptidase (GGT) is the only enzyme known that can cleave the gamma-peptide bond between glutamate and cysteine in glutathione, and is therefore a key step in glutathione degradation. There are three functional GGT genes in Arabidopsis, two of which are considered here. GGT1 and GGT2 are apoplastic, associated with the plasma membrane and/or cell wall. RNA blots and analysis of enzyme activity in knockout mutants suggest that GGT1 is expressed most strongly in leaves but is found throughout the plant. A GGT1::GUS fusion construct showed expression only in vascular tissue, specifically the phloem of the mid-rib and minor veins of leaves, roots and flowers. This localization was confirmed in leaves by laser microdissection. GGT2 expression is limited to embryo, endosperm, outer integument, and a small portion of the funiculus in developing siliques. The ggt2 mutants had no detectable phenotype, while the ggt1 knockouts were smaller and flowered sooner than wild-type. In ggt1 plants, the cotyledons and older leaves yellowed early, and GSSG, the oxidized form of glutathione, accumulated in the apoplastic space. These observations suggest that GGT1 is important in preventing oxidative stress by metabolizing extracellular GSSG, while GGT2 might be important in transporting glutathione into developing seeds.

The Wnt/b-catenin signaling pathway is critical in both cellular proliferation and organismal development. However, how the b-catenin degradation complex is inhibited upon Wnt activation remains unclear. Using a directed RNAi screen we find that protein phosphatase 1 (PP1), a ubiquitous serine/threonine phosphatase, is a novel potent positive physiologic regulator of the Wnt/bcatenin signaling pathway. PP1 expression synergistically activates, and inhibition of PP1 inhibits, Wnt/b-catenin signaling in Drosophila and mammalian cells as well as in Xenopus embryos. The data suggest that PP1 controls Wnt signaling through interaction with, and regulated dephosphorylation of, axin. Inhibition of PP1 leads to enhanced phosphorylation of specific sites on axin by casein kinase I. Axin phosphorylation markedly enhances the binding of glycogen synthase kinase 3, leading to a more active b-catenin destruction complex. Wnt-regulated changes in axin phosphorylation, mediated by PP1, may therefore determine b-catenin transcriptional activity. Specific inhibition of PP1 in this pathway may offer therapeutic approaches to disorders with increased b-catenin signaling.

An early step in establishing left-right (LR) symmetry in zebrafish is the generation of asymmetric fluid flow by Kupffer’s vesicle (KV). As a result of fluid flow, a signal is generated and propagated from the KV to the left lateral plate mesoderm, activating a transcriptional response of Nodal expression in the left lateral plate mesoderm (LPM). The mechanisms and molecules that aid in this transfer of information from the KV to the left LPM are still not clear. Here we provide several lines of evidence demonstrating a role for a member of the TGFβ family member, Dvr1, a zebrafish Vg1 ortholog. Dvr1 is expressed bilaterally between the KV and the LPM. Knockdown of Dvr1 by morpholino causes dramatically reduced or absent expression of southpaw (spaw, a Nodal homolog), in LPM, and corresponding loss of downstream Lefty (lft1 and lft) expression, and aberrant brain and heart LR patterning. Dvr1 morphant embryos have normal KV morphology and function, normal expression of southpaw (spaw) and charon (cha) in the peri-KV region and normal expression of a variety of LPM markers in LPM. Additionally, Dvr1 knockdown does not alter the capability of LPM to respond to signals that initiate and propagate spaw expression. Co-injection experiments in Xenopus and zebrafish indicate that Dvr1 and Spaw can enhance each other’s ability to activate the Nodal response pathway and co-immunoprecipitation experiments reveal differential relationships among activators and inhibitors in this pathway. These results indicate that Dvr1 is responsible for enabling the transfer of a left-right signal from KV to the LPM.

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