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- A novel serotonin-secreting cell type regulates ciliary motility in the mucociliary epidermis of Xenopus tadpoles. [JOURNAL ARTICLE]
- Development 2014 Mar 5.
The embryonic skin of Xenopus tadpoles serves as an experimental model system for mucociliary epithelia (MCE) such as the human airway epithelium. MCEs are characterized by the presence of mucus-secreting goblet and multiciliated cells (MCCs). A third cell type, ion-secreting cells (ISCs), is present in the larval skin as well. Synchronized beating of MCC cilia is required for directional transport of mucus. Here we describe a novel cell type in the Xenopus laevis larval epidermis, characterized by serotonin synthesis and secretion. It is termed small secretory cell (SSC). SSCs are detectable at early tadpole stages, unlike MCCs and ISCs, which are specified at early neurulation. Subcellularly, serotonin was found in large, apically localized vesicle-like structures, which were entirely shed into the surrounding medium. Pharmacological inhibition of serotonin synthesis decreased the velocity of cilia-driven fluid flow across the skin epithelium. This effect was mediated by serotonin type 3 receptor (Htr3), which was expressed in ciliated cells. Knockdown of Htr3 compromised flow velocity by reducing the ciliary motility of MCCs. SSCs thus represent a distinct and novel entity of the frog tadpole MCE, required for ciliary beating and mucus transport across the larval skin. The identification and characterization of SSCs consolidates the value of the Xenopus embryonic skin as a model system for human MCEs, which have been known for serotonin-dependent regulation of ciliary beat frequency.
- Symmetry breakage in the frog Xenopus: Role of Rab11 and the ventral-right blastomere. [JOURNAL ARTICLE]
- Genesis 2014 Mar 2.
Vertebrates display asymmetric arrangements of inner organs such as heart and stomach. The Nodal signaling cascade in the left lateral plate mesoderm in all cases directs asymmetric morphogenesis and placement during organogenesis. Mechanisms that lead up to left-asymmetric Nodal induction seem to differ between the vertebrates. Cilia produce a leftward extracellular fluid flow in zebrafish, medaka, mouse, rabbit and Xenopus embryos during neurulation. In Xenopus, earlier asymmetric cues were described. Some, such as Rab11, apparently act in the zygote. Others were efficiently manipulated in ventral-right cells at the 4-cell stage, a lineage presumably independent of the ciliated gastrocoel roof plate (GRP) during neurulation. Here we show that 1- and 4-cell manipulations of Rab11 showed equal low efficiencies of left-right disturbances. We also re-evaluated the lineage of the GRP. By tracing back future ciliated cells from the gastrula to the 4-cell stage, we show that ventral cells contribute to ciliated sensory cells at the border of the GRP. Knockdown of the Nodal inhibitor Coco in the ventral right lineage resulted in embryos with ectopic right-sided Nodal and Pitx2c expression. Together, these experiments support a cilia-based mechanism of symmetry breakage in the frog Xenopus. © 2014 Wiley Periodicals, Inc.
- A zinc transporter gene required for development of the nervous system. [Journal Article]
- Commun Integr Biol 2013 Nov 1; 6(6):e26207.
The essentiality of zinc for normal brain development is well established. It has been suggested that primary and secondary zinc deficiencies can contribute to the occurrence of numerous human birth defects, including many involving the central nervous system. In a recent study, we searched for zinc transporter genes that were critical for neurodevelopment. We confirmed that ZIP12 is a zinc transporter encoded by the gene slc39a12 that is highly expressed in the central nervous systems of human, mouse, and frog (Xenopus tropicalis).Using loss-of-function methods, we determined that ZIP12 is required for neuronal differentiation and neurite outgrowth and necessary for neurulation and embryonic viability. These results highlight an essential need for zinc regulation during embryogenesis and nervous system development. We suggest that slc39a12 is a candidate gene for inherited neurodevelopmental defects in humans.
- Retained medullary cord confirmed by intraoperative neurophysiological mapping. [JOURNAL ARTICLE]
- Childs Nerv Syst 2014 Feb 23.
A retained medullary cord (RMC) is a rare dysraphic malformation, recently described as a late arrest of secondary neurulation. RMC is also a severely tethering lesion. The critical role of intraoperative neurophysiology to safely manage a RMC has been only anecdotally reported.We describe the case of a RMC in a 1.5-year-old child with Currarino syndrome. At surgery, an apparently normal-looking spinal cord, stretched and tethered by a lipoma to the level of S2-S3, was observed. The border between the functional conus and the non functional RMC was defined through neurophysiological mapping. The cord was sharply interrupted at this level and untethered. A specimen was sent for pathology, which confirmed the presence of glial and neural elements. The post-operative neurological exam was normal.Neurosurgical procedure for RMC should only be rendered with intraoperative neurophysiological mapping, as the anatomical judgment would not suffice to allow a safe cutting of these "normal-looking" neural structures.
- The emerging roles of ribosome biogenesis in craniofacial development. [REVIEW]
- Front Physiol 2014.:26.
Neural crest cells (NCCs) are a transient, migratory cell population, which originates during neurulation at the neural folds and contributes to the majority of tissues, including the mesenchymal structures of the craniofacial skeleton. The deregulation of the complex developmental processes that guide migration, proliferation, and differentiation of NCCs may result in a wide range of pathological conditions grouped together as neurocristopathies. Recently, due to their multipotent properties neural crest stem cells have received considerable attention as a possible source for stem cell based regenerative therapies. This exciting prospect underlines the need to further explore the developmental programs that guide NCC differentiation. This review explores the particular importance of ribosome biogenesis defects in this context since a specific interface between ribosomopathies and neurocristopathies exists as evidenced by disorders such as Treacher-Collins-Franceschetti syndrome (TCS) and Diamond-Blackfan anemia (DBA).
- Abelson phosphorylation of CLASP2 modulates its association with microtubules and actin. [JOURNAL ARTICLE]
- Cytoskeleton (Hoboken) 2014 Feb 12.
The Abelson (Abl) non-receptor tyrosine kinase regulates the cytoskeleton during multiple stages of neural development, from neurulation, to the articulation of axons and dendrites, to synapse formation and maintenance. We previously showed that Abl is genetically linked to the microtubule (MT) plus end tracking protein (+TIP) CLASP in Drosophila. Here we show in vertebrate cells that Abl binds to CLASP and phosphorylates it in response to serum or PDGF stimulation. In vitro, Abl phosphorylates CLASP with a Km of 1.89 μM, indicating that CLASP is a bona fide substrate. Abl-phosphorylated tyrosine residues that we detect in CLASP by mass spectrometry lie within previously mapped F-actin and MT plus end interaction domains. Using purified proteins, we find that Abl phosphorylation modulates direct binding between purified CLASP2 with both MTs and actin. Consistent with these observations, Abl-induced phosphorylation of CLASP2 modulates its localization as well as the distribution of F-actin structures in spinal cord growth cones. Our data suggest that the functional relationship between Abl and CLASP2 is conserved and provides a means to control the CLASP2 association with the cytoskeleton. © 2014 Wiley Periodicals, Inc.
- Expression and function of transcription factor cMyb during cranial neural crest development. [JOURNAL ARTICLE]
- Mech Dev 2014 Feb 6.
The transcription factor cMyb has well known functions in vertebrate hematopoiesis, but little was known about its distribution or function at early developmental stages. Here, we show that cMyb transcripts are present at the neural plate during gastrulation in chick embryos. cMyb expression then resolves to the cranial neural folds and is maintained in early migrating cranial neural crest cells during and after neurulation. Morpholino-mediated knock-down of cMyb reduces expression of Pax7 and Twist at the neural plate border, as well as reducing expression of neural crest specifier gene Slug/Snail2 and completely eliminating expression of Ets1. On the other hand, its loss results in abnormal maintenance of Zic1, but little or no effect on other neural crest specifier genes like FoxD3 or Sox9. These results place cMyb in a critical hierarchical position within the cranial neural crest cell gene regulatory network, likely directly inhibiting Zic1 and upstream of Ets1 and some, but not all, neural crest specifier genes.
- Time-lapse X-ray phase-contrast microtomography for in vivo imaging and analysis of morphogenesis. [Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.]
- Nat Protoc 2014 Feb; 9(2):294-304.
X-ray phase-contrast microtomography (XPCμT) is a label-free, high-resolution imaging modality for analyzing early development of vertebrate embryos in vivo by using time-lapse sequences of 3D volumes. Here we provide a detailed protocol for applying this technique to study gastrulation in Xenopus laevis (African clawed frog) embryos. In contrast to μMRI, XPCμT images optically opaque embryos with subminute temporal and micrometer-range spatial resolution. We describe sample preparation, culture and suspension of embryos, tomographic imaging with a typical duration of 2 h (gastrulation and neurulation stages), intricacies of image pre-processing, phase retrieval, tomographic reconstruction, segmentation and motion analysis. Moreover, we briefly discuss our present understanding of X-ray dose effects (heat load and radiolysis), and we outline how to optimize the experimental configuration with respect to X-ray energy, photon flux density, sample-detector distance, exposure time per tomographic projection, numbers of projections and time-lapse intervals. The protocol requires an interdisciplinary effort of developmental biologists for sample preparation and data interpretation, X-ray physicists for planning and performing the experiment and applied mathematicians/computer scientists/physicists for data processing and analysis. Sample preparation requires 9-48 h, depending on the stage of development to be studied. Data acquisition takes 2-3 h per tomographic time-lapse sequence. Data processing and analysis requires a further 2 weeks, depending on the availability of computing power and the amount of detail required to address a given scientific problem.
- TGF-βs and Smads activities at the site of failed neural tube in the human embryos. [Journal Article]
- Turk Neurosurg 2013; 23(6):693-9.
Transforming growth factor β (TGF-β) and Smads control intracellular signaling pathways in neurulation. Although previously reported similar experimental animal studies, the aim of this human study is to investigate the expression of TGF-β (1,2,3) and Smads (1,2,3,6,7) in aborted human fetuses with myeloschisis. MATERIAL andTwelve human fetuses with neural tube defect were obtained. They were stained with antibodies against TGF-β1, TGF-β2, TGF-β3, Smad (1,2,3), Smad 6 and Smad 7 using the indirect immunohistochemical technique.We noted mild immune reactivity of TGF-β1 and TGF-β2 in the open neural plate, motor neurons and surrounding tissue. Strong immune reactivity of TGF-β3 was shown in only open neural plate and surrounding tissue. Immunoreactivity of all Smads noted negative except Smad7.These results suggested at the site where the neural tube failed to close, TGF-β 1,2 and Smads 1,2,3,6 do not continue their activity and decrease with internal timing of embryonic development. Additionally ectodermal layers are considered by embryo as "not closed wound" and TGF-β3 activity may be an effort to repair the failed closure.
- Sip1 mediates an E-cadherin-to-N-cadherin switch during cranial neural crest EMT. [Journal Article, Research Support, N.I.H., Extramural]
- J Cell Biol 2013 Dec 9; 203(5):835-47.
The neural crest, an embryonic stem cell population, initially resides within the dorsal neural tube but subsequently undergoes an epithelial-to-mesenchymal transition (EMT) to commence migration. Although neural crest and cancer EMTs are morphologically similar, little is known regarding conservation of their underlying molecular mechanisms. We report that Sip1, which is involved in cancer EMT, plays a critical role in promoting the neural crest cell transition to a mesenchymal state. Sip1 transcripts are expressed in premigratory/migrating crest cells. After Sip1 loss, the neural crest specifier gene FoxD3 was abnormally retained in the dorsal neuroepithelium, whereas Sox10, which is normally required for emigration, was diminished. Subsequently, clumps of adherent neural crest cells remained adjacent to the neural tube and aberrantly expressed E-cadherin while lacking N-cadherin. These findings demonstrate two distinct phases of neural crest EMT, detachment and mesenchymalization, with the latter involving a novel requirement for Sip1 in regulation of cadherin expression during completion of neural crest EMT.