Hypoxia inhibits lymphatic thoracic duct formation in zebrafish.

Hypoxia promotes blood vessel growth through up-regulation of pro-angiogenic pathways but its role on the lymphatic system remains unclear. The homeobox transcription factor Prox1 is a master control gene for generating lymphatic endothelial cells (LECs) and is up-regulated by hypoxia-inducible factors in mammals. While vascular endothelial growth factor A (VEGFA) is critical for angiogenesis, VEGFC and its receptor VEGF receptor-3 (VEGFR-3) are essential for the initial sprouting and directed migration as well as for the subsequent survival of LECs. The aim of this study was to determine the effects of hypoxia on the development of the lymphatic system in zebrafish. Zebrafish embryos were obtained from Tg(SAGFF27C; UAS:GFP) animals carrying a lymphatic reporter gene coupled to green fluorescent protein (GFP). Exposure of 1-day old zebrafish embryos to hypoxic conditions (5% O2) for 24 h inhibited thoracic duct formation (-27%, p < 0.0001). Hypoxia inhibited the expression of pro-lymphangiogenic factors prox1a, vegfc and vegfr-3. This inhibition was relieved after re-oxygenation. On the other hand, hypoxia increased the expression of vegfa, a pro-angiogenic factor. In conclusion, hypoxia has opposite effects on vascular development in zebrafish, inhibiting the development of the lymphatic vascular system while promoting the development of the blood vascular system.

Normal interstitial flow is critical for developmental lymphangiogenesis in the zebrafish.

BACKGROUND: The lymphatic system plays a critical role in the body's fluid and protein homeostasis, immune regulation, and dietary fat absorption. One of the major pathologies of the lymphatic system is primary lymphedema, which occurs in approximately 0.6% of live births and is caused by missing or impaired lymphatic vessels. Although there is a great need for medical intervention into diseases of the lymphatic system, very little is known about its development or how it maintains integrity over time. Recent studies have suggested that biophysical components, such as local extracellular fluid flow, may be important factors during initiation of lymphangiogenesis. We hypothesize that interstitial fluid flow functions as an important morphoregulator during developmental lymphangiogenesis. METHODS AND RESULTS: In the present study we use pharmacological agents and a mutant fish line to modulate interstitial flow. Our data confirm that a sufficient increase or decrease in interstitial flow can profoundly affect lymphatic patterning and may result in a lymphedema-like phenotype. Proper interstitial flow appears to be necessary during LEC migration for proper lymphatic development. CONCLUSIONS: These results support the contention that interstitial flow is an important morphoregulator of developmental lymphangiogenesis.

Role of synectin in lymphatic development in zebrafish and frogs.

The molecular basis of lymphangiogenesis remains incompletely characterized. Here, we document a novel role for the PDZ domain-containing scaffold protein synectin in lymphangiogenesis using genetic studies in zebrafish and tadpoles. In zebrafish, the thoracic duct arises from parachordal lymphangioblast cells, which in turn derive from secondary lymphangiogenic sprouts from the posterior cardinal vein. Morpholino knockdown of synectin in zebrafish impaired formation of the thoracic duct, due to selective defects in lymphangiogenic but not angiogenic sprouting. Synectin genetically interacted with Vegfr3 and neuropilin-2a in regulating lymphangiogenesis. Silencing of synectin in tadpoles caused lymphatic defects due to an underdevelopment and impaired migration of Prox-1(+) lymphatic endothelial cells. Molecular analysis further revealed that synectin regulated Sox18-induced expression of Prox-1 and vascular endothelial growth factor C-induced migration of lymphatic endothelial cells in vitro. These findings reveal a novel role for synectin in lymphatic development.

Fatal bilateral chylothorax in mice lacking the integrin alpha9beta1.

Members of the integrin family of adhesion receptors mediate both cell-cell and cell-matrix interactions and have been shown to play vital roles in embryonic development, wound healing, metastasis, and other biological processes. The integrin alpha9beta1 is a receptor for the extracellular matrix proteins osteopontin and tenacsin C and the cell surface immunoglobulin vascular cell adhesion molecule-1. This receptor is widely expressed in smooth muscle, hepatocytes, and some epithelia. To examine the in vivo function of alpha9beta1, we have generated mice lacking expression of the alpha9 subunit. Mice homozygous for a null mutation in the alpha9 subunit gene appear normal at birth but develop respiratory failure and die between 6 and 12 days of age. The respiratory failure is caused by an accumulation of large volumes of pleural fluid which is rich in triglyceride, cholesterol, and lymphocytes. alpha9(-/-) mice also develop edema and lymphocytic infiltration in the chest wall that appears to originate around lymphatics. alpha9 protein is transiently expressed in the developing thoracic duct at embryonic day 14, but expression is rapidly lost during later stages of development. Our results suggest that the alpha9 integrin is required for the normal development of the lymphatic system, including the thoracic duct, and that alpha9 deficiency could be one cause of congenital chylothorax.

[Catecholamine content in the wall of the thoracic duct of the dog during postnatal development]. / Soderzhanie katekholaminov v stenke grudnogo limfaticheskogo protoka sobaki v protsesse postnatal'nogo razvitiia.

Studies have been made on the content of catecholamines (norepinephrine, adrenaline, dihydroxyphenylalanine) in the wall of the thoracic lymphatic duct of puppies during their first 3 months of postnatal life. It was found that within this period, the content of norepinephrine increases, that of adrenaline remains unchanged, whereas dihydroxyphenylalanine is detected only in animals of the first month. The increase in norepinephrine content indicates gradual maturation of the adrenergic innervation in the wall of the lymphatic duct.

[Development of the contractile activity of the thoracic duct in dogs in postnatal ontogenesis]. / Razvitie sokratitel'noi aktivnosti grudnogo limfaticheskogo protoka u sobak v postnatal'nom ontogeneze.

It has been demonstrated that the thoracic lymph duct in newborn puppies exhibits only tonic (spontaneous) contractile activity. Rhythmic activity in the duct appears at the age of 2 1/2-3 months.

[Structure of the wall of thoracic lymphatic duct of dogs in postnatal ontogeny]. / Izuchenie stroeniia stenki grudnogo limfaticheskogo protoka u sobak v postnatal'nom ontogeneze.

Light and electronmicroscopic studies have been made on the structure of the wall of the thoracic lymph duct in puppies within 3 months of their postnatal life. It was shown that differentiation and specialization of the smooth muscle cells is accomplished in the main features to the 3rd month of postnatal life. Within this period, the number of the nervous fibers increases, and their linking to the media becomes more close. Absence of dense neuro-muscular contacts indicates distant pattern of the effect of neuromediators on the effector cells. The data obtained demonstrate that during postnatal ontogenesis of dogs changes take place in the barrier properties of the wall of the lymph duct, as well as the formation of morphological substrate for active contractile activity.