Stored elastic bending tension as a mediator of embryonic body folding.

During development, amniote vertebrate embryos transform from a flat sheet into a three-dimensional cylindrical form through ventral folding of the lateral sides of the sheet (the lateral plate [LP]) and their fusion in the ventral midline. Using a chick embryo slice system, we find that the flat stage is actually a poised balance of opposing dorsal and ventral elastic bending tensions. An intact extracellular matrix (ECM) is required for generating tension, as localized digestion of ECM dissipates tension, while removal of endoderm or ectoderm layers has no significant effect.

An atypical basement membrane forms a midline barrier during left-right asymmetric gut development in the chicken embryo.

Correct intestinal morphogenesis depends on the early embryonic process of gut rotation, an evolutionarily conserved program in which a straight gut tube elongates and forms into its first loops. However, the gut tube requires guidance to loop in a reproducible manner. The dorsal mesentery (DM) connects the gut tube to the body and directs the lengthening gut into stereotypical loops via left-right (LR) asymmetric cellular and extracellular behavior.

A morphogenetic wave in the chick embryo lateral mesoderm generates mesenchymal-epithelial transition through a 3D-rosette intermediate.

Formation of epithelia through mesenchymal-epithelial transition (MET) is essential for embryonic development and for many physiological and pathological processes. This study investigates MET in vivo in the chick embryo lateral mesoderm, where a multilayered mesenchyme transforms into two parallel epithelial sheets that constitute the coelomic lining of the embryonic body cavity. Prior to MET initiation, mesenchymal cells exhibit non-polarized distribution of multiple polarity markers, albeit not aPKC.

Regulation of aortic morphogenesis and VE-cadherin dynamics by VEGF.

In amniote vertebrates, the definitive dorsal aorta is formed by the fusion of two primordial aortic endothelial tubes. Formation of the definitive dorsal aorta requires extensive cellular migrations and rearrangements of the primordial tubes in order to generate a single vessel located at the embryonic ventral midline. This study examines the role of VEGF signaling in the generation of the definitive dorsal aorta.

Hedgehog Signaling Regulates Epithelial Morphogenesis to Position the Ventral Embryonic Midline.

Despite much progress toward understanding how epithelial morphogenesis is shaped by intra-epithelial processes including contractility, polarity, and adhesion, much less is known regarding how such cellular processes are coordinated by extra-epithelial signaling. During embryogenesis, the coelomic epithelia on the two sides of the chick embryo undergo symmetrical lengthening and thinning, converging medially to generate and position the dorsal mesentery (DM) in the embryonic midline. We find that Hedgehog signaling, acting through downstream effectors Sec5 (ExoC2), an exocyst complex component, and RhoU (Wrch-1), a small GTPase, regulates coelomic epithelium morphogenesis to guide DM midline positioning.

Establishment of the Visceral Embryonic Midline Is a Dynamic Process that Requires Bilaterally Symmetric BMP Signaling.

The vertebrate body plan contains both dorsal and ventral midline structures. While dorsal midline structures have been extensively studied, formation of ventral midline structures, and how they become aligned with the dorsal midline, is a fundamental aspect of vertebrate development that is poorly understood. This study uses the chick dorsal mesentery (DM) as a model for investigating the formation of ventral midline structures.

Wnt signaling orients the proximal-distal axis of chick kidney nephrons.

The nephron is the fundamental structural and functional unit of the kidney. Each mature nephron is patterned along a proximal-distal axis, with blood filtered at the proximal end and urine emerging from the distal end. In order to filter the blood and produce urine, specialized structures are formed at specific proximal-distal locations along the nephron, including the glomerulus at the proximal end, the tubule in the middle and the collecting duct at the distal end.

Collective cell migration of the nephric duct requires FGF signaling.

Background: During the course of development, the vertebrate nephric duct (ND) extends and migrates from the place of its initial formation, adjacent to the anterior somites, until it inserts into the bladder or cloaca in the posterior region of the embryo. The molecular mechanisms that guide ND migration are poorly understood.

Results: A novel Gata3-enhancer-Gfp-based chick embryo live imaging system was developed that permits documentation of ND migration at the individual cell level for the first time.

Generation of the podocyte and tubular components of an amniote kidney: timing of specification and a role for Wnt signaling.

Kidneys remove unwanted substances from the body and regulate the internal body environment. These functions are carried out by specialized cells (podocytes) that act as a filtration barrier between the internal milieu and the outside world, and by a series of tubules and ducts that process the filtrate and convey it to the outside. In the kidneys of amniote vertebrates, the filtration (podocyte) and tubular functions are tightly integrated into functional units called nephrons.

Parallel waves of inductive signaling and mesenchyme maturation regulate differentiation of the chick mesonephros.

The mesonephros is a linear kidney that, in chicken embryos, stretches between the axial levels of the 15th to the 30th somites. Mesonephros differentiation proceeds from anterior to posterior and is dependent on signals from the nephric duct, which migrates from anterior to posterior through the mesonephric region. If migration of the nephric duct is blocked, markers of tubule differentiation, including Lhx1 and Wnt4, are not activated posterior to the blockade.

A role for Vg1/Nodal signaling in specification of the intermediate mesoderm.

The intermediate mesoderm (IM) is the embryonic source of all kidney tissue in vertebrates. The factors that regulate the formation of the IM are not yet well understood. Through investigations in the chick embryo, the current study identifies and characterizes Vg1/Nodal signaling (henceforth referred to as 'Nodal-like signaling') as a novel regulator of IM formation.

Analysis of nephric duct specification in the avian embryo.

Vertebrate kidney tissue exhibits variable morphology that in general increases in complexity when moving from anterior to posterior along the body axis. The nephric duct, a simple unbranched epithelial tube, is derived in the avian embryo from a rudiment located in the anterior intermediate mesoderm (IM) adjacent to somites 8 to 10. Using quail-chick chimeric embryos, the current study finds that competence to form nephric duct is fixed when IM precursor cells are still located in the primitive streak, significantly before the onset of duct differentiation.

Promotion of avian endothelial cell differentiation by GATA transcription factors.

In the avian embryo, endothelial cells originate from several sources, including the lateral plate and somite mesoderm. In this study, we show that Gata transcription factors are expressed in the lateral plate and in vasculogenic regions of the avian somite and are able to promote a vascular endothelial fate when ectopically expressed in somite precursors. A fusion of GATA4 to the transcriptional activator VP16 promoted endothelium formation, indicating that GATA transcription factors promote vasculogenesis via activation of downstream targets, while a fusion of GATA4 to the transcriptional repressor engrailed repressed expression of Vascular Endothelial Growth Factor Receptor 2, a marker of endothelial precursors.

Multimodality optical imaging of embryonic heart microstructure.

Study of developmental heart defects requires the visualization of the microstructure and function of the embryonic myocardium, ideally with minimal alterations to the specimen. We demonstrate multiple endogenous contrast optical techniques for imaging the Xenopus laevis tadpole heart. Each technique provides distinct and complementary imaging capabilities, including: 1.

Early molecular effects of ethanol during vertebrate embryogenesis.

Fetal alcohol spectrum disorder (FASD) is the combination of developmental, morphological, and neurological defects that result from exposing human embryos to ethanol (EtOH). Numerous embryonic structures are affected, leading to a complex viable phenotype affecting among others, the anterior/posterior axis, head, and eye formation. Recent studies have provided evidence suggesting that EtOH teratogenesis is mediated in part through a reduction in retinoic acid (RA) levels, targeting mainly the embryonic organizer (Spemann's organizer) and its subsequent functions.

Ethanol exposure affects gene expression in the embryonic organizer and reduces retinoic acid levels.

Fetal Alcohol Spectrum Disorder (FASD) is a set of developmental malformations caused by alcohol consumption during pregnancy. Fetal Alcohol Syndrome (FAS), the strongest manifestation of FASD, results in short stature, microcephally and facial dysmorphogenesis including microphthalmia. Using Xenopus embryos as a model developmental system, we show that ethanol exposure recapitulates many aspects of FAS, including a shortened rostro-caudal axis, microcephally and microphthalmia.

The competence of marginal zone cells to become Spemann's organizer is controlled by Xcad2.

The organizer in vertebrate embryos is responsible for the formation of the primary body axis. In amphibian embryos, the organizer forms in the dorsal marginal zone (prospective dorsal mesoderm) at a location determined by the point of sperm entry. Using inducible versions of axis-inducing proteins, it has been shown that, irrespective of the mode of secondary axis induction, organizer formation in the ventral marginal zone is temporally restricted from the midblastula transition to the onset of gastrulation.