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.

Disruption of the aortic wall by coelomic lining-derived mesenchymal cells accompanies the onset of aortic hematopoiesis.

In vertebrates, definitive hematopoietic stem cells (HSCs) first emerge in the ventral wall of the aorta in the Aorta-Gonad-Mesonephros (AGM) region of the embryo, where they differentiate from a specialized type of endothelium termed Hemogenic Endothelium (HE). While the transition from HE to hematopoietic tissue has received much experimental attention, much less is known regarding generation of HE itself. The current study investigates the emergence of the HE in the chick embryo aorta.

Nkx2.5 marks angioblasts that contribute to hemogenic endothelium of the endocardium and dorsal aorta.

Novel regenerative therapies may stem from deeper understanding of the mechanisms governing cardiovascular lineage diversification. Using enhancer mapping and live imaging in avian embryos, and genetic lineage tracing in mice, we investigated the spatio-temporal dynamics of cardiovascular progenitor populations. We show that expression of the cardiac transcription factor marks a mesodermal population outside of the cardiac crescent in the extraembryonic and lateral plate mesoderm, with characteristics of hemogenic angioblasts.

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.

Transport of membrane-bound mineral particles in blood vessels during chicken embryonic bone development.

During bone formation in embryos, large amounts of calcium and phosphate are taken up and transported to the site where solid mineral is first deposited. The initial mineral forms in vesicles inside osteoblasts and is deposited as a highly disordered calcium phosphate phase. The mineral is then translocated to the extracellular space where it penetrates the collagen matrix and crystallizes.

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.