Mural cells of the vascular system include vascular smooth muscle cells (SMCs) and pericytes whose role is to stabilize and/or provide contractility to blood vessels. One of the earliest markers of mural cell development in vertebrates is α smooth muscle actin (acta2; αsma), which is expressed by pericytes and SMCs. In vivo models of vascular mural cell development in zebrafish are currently lacking, therefore we developed two transgenic zebrafish lines driving expression of GFP or mCherry in acta2-expressing cells. These transgenic fish were used to trace the live development of mural cells in embryonic and larval transgenic zebrafish. acta2:EGFP transgenic animals show expression that largely mirrors native acta2 expression, with early pan-muscle expression starting at 24 hpf in the heart muscle, followed by skeletal and visceral muscle. At 3.5 dpf, expression in the bulbus arteriosus and ventral aorta marks the first expression in vascular smooth muscle. Over the next 10 days of development, the number of acta2:EGFP positive cells and the number of types of blood vessels associated with mural cells increases. Interestingly, the mural cells are not motile and remain in the same position once they express the acta2:EGFP transgene. Taken together, our data suggests that zebrafish mural cells develop relatively late, and have little mobility once they associate with vessels.

Smooth muscle is important for the contractility and elasticity of visceral organs. The zebrafish is an excellent model for understanding embryonic development, yet due to a lack of appropriate markers, visceral smooth muscle development remains poorly characterized. Here, we develop markers and trace the development of gut and swim bladder smooth muscle in embryonic and juvenile fish. The first smooth muscle marker we detect in the vicinity of the gut is the myoblast marker nonmuscle myosin heavy chain-b at 50 hours postfertilization (hpf), followed by the early smooth muscle markers SM22␣-b, and ␣-smooth muscle actin at 56 and 60 hpf, respectively. Markers of more differentiated smooth muscle, smoothelin-b and cpi-17, appear by 3 days postfertilization (dpf). Tropomyosin, a relatively late marker, is first expressed at 4 dpf. We find that smooth muscle marker expression in the swim bladder follows the same sequence of marker expression as the gut, but markers have a temporal delay reflecting the later formation of swim bladder smooth muscle. Developmental Dynamics 236:1623-1632, 2007.

Spleen tyrosine kinase (Syk) plays critical roles in B-cell and T-cell development, the maintenance of vascular integrity, and proper partitioning of the blood vascular and lymphatic vascular system. Here, we utilize the zebrafish as an in vivo system to demonstrate novel roles for Syk and the related kinase Zeta associated protein (Zap-70) in promoting angioblast migration. Partial knockdown of either gene results in early angiogenic delay of the intersegmental vessels, dorsal intersegmental vessel patterning defects, and partial loss of the thoracic duct. Higher dose knockdown of both genes results in little to no angiogenic sprouting of the intersegmental vessels, a phenotype which resembles knockdown of vegfa. Di-phosphorylated ERK, an effector of the vegfa pathway, is also downregulated in the aorta of syk:zap double morphants. Over-expression of syk under the control of a blood-specific or vascular-specific promoter rescues sprouting defects after loss of vegfa. Together these results suggest that syk and zap-70 function redundantly in an early progenitor to promote the migration of intersegmental vessel angioblasts and lymphangioblasts that contribute to the thoracic duct, either downstream of, or in parallel to vegfa.

He then argues for the replacement of exp (EGj(xj)) by an appropriate multivariate normal distribution, and arrives via this route at the final result 42 Ad 1 / q1/G + 1/2 6MacArthur, R. H., "Fluctuations in animal populations and a measure of community stab)ility," Ecology, 35, 533-536 (1955). 7Dr. MacArthur has remarked that the units of P/B are biomass/life span 1 biomass life span and that P/B is an appropriately weighed harmonic mean of the life spans of the species of the community.During the course of embryonic development and differentiation, cells become distinguishable from each other on the basis of their arrays of proteins.' Since the appearance of specific proteins occurs in both a spatially and temporally restricted fashion, it appears reasonable to assume that the flow of genetic information from DNA is being regulated in a precise fashion. According to current theories of protein synthesis, this could be interpreted as being due to differential synthesis of messenger RNA. Models have been constructed for the regulation of gene expression based on regulator genes2 or histones.3 Evidence derived from experiments with actinomycin D have suggested that there is a temporal sequence of synthesis of the tissue-specific RNA molecules responsible for differentiation.4Any modification at the level of the chromatin or DNA would be expected to be reflected in the synthesis of messenger RNA. In the present study the ability to prime for the synthesis of DNA-dependent RNA was determined for both DNA and chromatin isolated from frog embryos and adult frogs (Rana pipiens). The priming ability was determined with RNA polymerase isolated from Micrococcus lysodeiktijus which synthesizes RNA complementary to the DNA primer when the four ribonucleoside triphosphates and MnCl2 are present., The use of chromatin has the advantage of retaining any regulators of RNA synthesis which may be associated wi th the chromatin and allows comparison with the DNA component itself.

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