To investigate molecular mechanisms controlling islet vascularization and revascularization after transplantation, we examined pancreatic expression of three families of angiogenic factors and their receptors in differentiating endocrine cells and adult islets. Using intravital lectin labeling, we demonstrated that development of islet microvasculature and establishment of islet blood flow occur concomitantly with islet morphogenesis. Our genetic data indicate that vascular endothelial growth factor (VEGF)-A is a major regulator of islet vascularization and revascularization of transplanted islets. In spite of normal pancreatic insulin content and ␤-cell mass, mice with ␤-cell-reduced VEGF-A expression had impaired glucose-stimulated insulin secretion. By vascular or diffusion delivery of ␤-cell secretagogues to islets, we showed that reduced insulin output is not a result of ␤-cell dysfunction but rather caused by vascular alterations in islets. Taken together, our data indicate that the microvasculature plays an integral role in islet function. Factors modulating VEGF-A expression may influence islet vascularity and, consequently, the amount of insulin delivered into the systemic circulation. Diabetes

Monoclonal antibodies (McAbs) against the myosin heavy chain (MHC) of adult chicken pectoralis muscle have been tested for reactivity with pectoralis myosin at selected stages of chick development in vivo and in vitro. Three such McAbs, MF 20 and MF 14, which bind to light meromyosin, and MF 30, which binds to myosin subfragment two ($2), were used to assay the appearance and accumulation of specific MHC epitopes with: (a) indirect, solid phase radioimmune assay (RIA), (b) immunoautoradiography, (c) immunofluorescence microscopy. McAb MF 20 bound strongly and equivalently to MHC at all stages of embryonic development in vivo. In contrast, the MF 30 epitope was barely detectable at 12 d of incubation but its concentration rose rapidly just before hatching. No detectable binding of MF 14 to pectoralis myosin could be measured during myogenesis in vivo until 1 wk after hatching. Immunofluorescence studies revealed that all three epitopes accumulate in the same myocytes of the developing pectoralis muscle. Since all three McAbs bound with high activity to native and denatured forms of myosin, it is unlikely that differential antibody reactivity can be explained by conformational changes in myosin during development in vivo. When myogenesis in vitro was monitored using the same McAbs, MF 20 bound to the MHC at all stages tested while reactivity of MF 30 and MF 14 with myosin from cultured muscle was never observed. Thus, this study demonstrates three different immunochemical states of the MHC during development in vivo of chick pectoralis muscle and the absence of later occurring immunochemical transitions in the MHC of cultured embryonic muscle.Isoforms of myosin have been demonstrated in adult (1,3,10,19,28,37) and embryonic (11,12,20,27,30,35,36) striated muscles of both birds and mammals. Three experimental formats have been used to substantiate these myosin variants within embryonic muscles. First, heterogeneity of myosin can be detected by electrophoresis on native pyrophosphate gels (14). Secondly, differences exist in the peptide maps obtained by limited proteolysis of adult and embryonic myosins (27,35,36). Finally, immunological dissimilarities exist between myosins isolated from homologous adult and embryonic muscles (11,12,20,26,35,36). Masaki and Yoshizaki (20) have demonstrated that myofibrils from embryonic chick pectoralis muscle bind antibodies specific for myosin of adult cardiac muscle, whereas similar myofibrils from adult pectoralis muscle do not. It was later proven that these cross-reactive determinants reside in the myosin heavy chain (MHC) subunit. More recently, Gauthier et al. (11,12) and Rubinstein and Kelley (26) have shown that developing rat skeletal myofibers contain MHCs which share antigenic homology with myosin isolated from both adult fast-and slow-twitch muscles. However, the adult myofibers bound specifically to either the "anti-slow" myosin or "anti-fast" myosin antiserum preparations. Immunochemical differences between myosin preparations purified from homologous em...

SummaryThe serosal mesothelium is a major source of smooth muscle cells of the gut vasculature

During mouse development, the sophisticated vascular network of the lung is established from embryonic day (E)Ϸ10.5 and continues to develop postnatally. This network is composed of endothelial cells enclosed by vascular smooth muscle, pericytes, and other mesenchymal cells. Recent in vivo lineage labeling studies in the developing heart and intestine suggest that some of the vascular smooth muscle cells arise from the surface mesothelium. In the developing lung, the Wilm's tumor 1 gene (Wt1) is expressed only in the mesothelial cells. Therefore, we lineage-labeled the mesothelium in vivo by using a Wt1-Cre transgene in combination with either Rosa26R lacZ , Rosa26R CAG-hPLAP , or Rosa26R EYFP reporter alleles. In all three cases, cells derived from lineage-labeled mesothelium are found inside the lung and as smooth muscle actin (SMA) and PDGF receptor-beta positive cells in the walls of pulmonary blood vessels. To corroborate this finding, we used 5-(and-6)-carboxy-2 ,7 -dichlorofluorescein diacetate, succinimidyl ester ''mixed isomers'' (CCFSE) dye to label mesothelial cells on the surface of the embryonic lung. Over the course of 72-h culture, dye-labeled cells also appear within the lung mesenchyme. Together, our data provide evidence that mesothelial cells serve as a source of vascular smooth muscle cells in the developing lung and suggest that a conserved mechanism applies to the development of blood vessels in all coelomic organs.lineage tracing ͉ blood vessel ͉ embryo ͉ pleura

Abstract-Formation of the coronary vessels is a fundamental event in heart development. Congenital abnormalities in the coronary system can have major deleterious effects on heart function. It is also possible that subtle variation in the patterning of coronary vessels has significant but uncharacterized effects on myocardial structure and function. In addition, generation of the coronary vascular system represents a complex system for analysis of regulation of cell fate determination, cell and epithelial migration, epithelial/mesenchymal transition, and patterning of a complex threedimensional structure. In this review, we present the descriptive embryology of this process as well as the recent data that shed light on the unique developmental mechanisms underlying generation of coronary vessels. This review also attempts to identify areas where additional research is needed and highlights the questions that must be answered for a meaningful understanding of coronary vessel development. Key Words: coronary vessels Ⅲ development P roblems of the coronary vascular system lead to major problems with the heart. Although the basic pathways taken by major coronary vessels over the surface of the heart are presented in cardiology textbooks, there is much variation in the pattern that is not well understood. Also, the enormity of the coronary system is not well appreciated as all, or nearly all, cardiac myocytes in mammalian hearts are in contact with a capillary and that the mammalian heart is one of the most vascularized organs of the body. Still, not a single cell that makes up the coronary system of the heart arises from the heart. Indeed, all the cells that make up the coronary system come from outside the heart are brought to the heart and differentiate into blood vessels only when they are in the heart. Indeed, all of this happens without ever tapping into the blood that courses through the heart lumen. The development and patterning of the coronary vascular system is a relatively unexplored area of vertebrate embryology that has important implications for human health.