Vascular system differentiation

Takahashi Y, Imanaka T, Takano T (1996) Spatial and temporal pattern of smooth muscle cell differentiation during develoment of the vascular system in the mouse embryo. Anat Embryol Berl 194 515-526... 

Patients with this most common form of homocystinuria show evidence of involvement of the eye, the skeletal system, the vascular system, and the brain. It is important to note that individuals with cystathionine P-synthase deficiency do not manifest any abnormalities at birth and that the affected pregnancies are uneventful. Thus, this disorder, as opposed to the more rare remethylation defect variants of homocystinuria (described below), is not usually part of the differential diagnosis of the catastrophically ill newborn. Ectopia lentis does not usually appear before the age of 3 years, but most patients have some manifestations by the age of 10. The initial recognition of ocular abnormahties may be an observation by parent or physician that the iris shakes, when the head is moved rapidly. While a predilection for... 

As the embryo matures, a procambial system differentiates throughout the hypocotyl and cotyledons. This system later gives rise to the components of the vascular system. This is foreshadowed by the development of differences in staining characteristics. Most commonly embryos have only differentiating xylem or phloem elements (Bisalputra and Esau 1964). 

Connective tissue in the vascular system plays an important role in maintenance of the intact vascular wall. Vitamins E and C influence the extracellular matrix (ECM) by their antioxidant functions. They bind to specific enzymes and act as cofactors and regulators with consequent modulation of vascular smooth muscle cell (VSMC) signal transduction and gene expression. The ability of vitamins E and C to influence VSMC proliferation, differentiation, and ECM production is important in the maintenance of intact vascular wall and in the repair of atherosclerotic lesions. Actively proliferating cells, but not quiescent cells, are susceptible to ascorbic acid, which inhibits cell division and promotes necrosis through its action on S-phase progression. 

The occurrence of nitrogenous compounds, particularly in cells in mature parts of the tree, may represent physical, chemical, and biological changes over the life cycle. For dead woody cells that compose the vascular system, the nitrogenous extractives may reflect the recent past history of the cells and the enzymes that have survived cellular differentiation. Labile enzymes are present in the secondary walls of differentiated reaction wood. Peroxidase, which is a universally stable enzyme in cell walls, cannot be detected histochemically in walls of dead cells (120). 

As long as an organism consists of only a few cells, communication and transport from one cell to another can take place without the need for systems specially designed for that purpose. If the number of cells and, thus, the size of the organism increases then special vascular systems must be developed. This need becomes the more imperative for the reason that specialization of individual cells in a multicellular organism is driven so far in quite different directions that an individual, highly differentiated cell, would be neither viable nor able to function without being supplemented by other differentiated cells of other kinds. 

Up to now we have only discussed xylem and must now bring the second component of the vascular system, the phloem, into the picture. Both the experiments of Wetmore on the elder and those of Jacobs on Coleus showed that the formation of phloem can be attained if IAA and sucrose are administered together. Once again we come across phenomena that are already familiar to us the unspecific effect of a phytohormone that can influence the most varied processes of differentiation, and the fact that combinations of the regulatory factors determine the kind of differentiation. 

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