ABSTRACT
Anatomical congruence of peripheral nerves and blood vessels is well recognized in a variety of tissues. Their physical proximity and similar branching patterns suggest that the development of these networks might be a coordinated process. Here we show that large diameter coronary veins serve as an intermediate template for distal sympathetic axon extension in the subepicardial layer of the dorsal ventricular wall of the developing mouse heart. Vascular smooth muscle cells (VSMCs) associate with large diameter veins during angiogenesis. In vivo and in vitro experiments demonstrate that these cells mediate extension of sympathetic axons via nerve growth factor (NGF). This association enables topological targeting of axons to final targets such as large diameter coronary arteries in the deeper myocardial layer. As axons extend along veins, arterial VSMCs begin to secrete NGF, which allows axons to reach target cells. We propose a sequential mechanism in which initial axon extension in the subepicardium is governed by transient NGF expression by VSMCs as they are recruited to coronary veins; subsequently, VSMCs in the myocardium begin to express NGF as they are recruited by remodeling arteries, attracting axons toward their final targets. The proposed mechanism underlies a distinct, stereotypical pattern of autonomic innervation that is adapted to the complex tissue structure and physiology of the heart.
Subject(s)
Coronary Vessels/physiology , Heart/embryology , Heart/innervation , Sympathetic Nervous System/embryology , Animals , Axons/physiology , Cells, Cultured , Chick Embryo , Coronary Vessels/embryology , Coronary Vessels/innervation , Embryo Culture Techniques , Embryo, Mammalian , Mice , Mice, Transgenic , Models, Biological , Muscle, Smooth, Vascular/embryology , Muscle, Smooth, Vascular/innervation , Muscle, Smooth, Vascular/metabolism , Pericardium/embryology , Pericardium/innervation , Sympathetic Nervous System/physiologyABSTRACT
BACKGROUND & AIMS: At the onset of liver development, cardiac mesoderm, septum transversum mesenchyme, and endothelial cells are involved in the specification and/or proliferation of hepatoblasts. After this initial stage, however, it is unclear which cells support the proliferation and differentiation of hepatocytes. Here we characterized the nature of mouse hepatic mesothelial cells (MCs) and investigated their role in organogenesis. METHODS: Using anti-podocalyxin-like protein 1 (PCLP1) and anti-mesothelin antibodies, we characterized MCs during liver development by immunohistochemistry, flow cytometry, and gene expression analysis. The possible role of MCs in hepatogenesis was investigated by in vitro culture and analysis of Wilms' tumor 1 homologue (WT1) knockout mice. RESULTS: PCLP1 was highly expressed in immature MCs, covering the surface of lobes. PCLP1 expression in MCs was down-regulated along with development, whereas mesothelin expression was up-regulated, indicating that these molecules distinguished developmental stages of MCs. The proliferation potential of MCs was high in the fetus and declined after birth. Fetal MCs expressed various growth factors and strongly enhanced the expansion of fetal hepatocytes in vitro, whereas differentiated MCs exhibited less growth factor expression, and differentiated MCs failed to enhance hepatocyte proliferation in vitro. In WT1-deficient embryos, hepatocyte proliferation was impaired due to defective MCs. CONCLUSIONS: The mesothelium is not only an inert protective sheet covering the parenchyma but also changes its characteristics dynamically during development and plays an active role in organogenesis by promoting expansion of parenchymal cells.
Subject(s)
Epithelial Cells/physiology , Hepatocytes/physiology , Liver/embryology , Animals , Cells, Cultured , Flow Cytometry , GPI-Linked Proteins , Membrane Glycoproteins/analysis , Mesothelin , Mice , Mice, Inbred C57BL , Sialoglycoproteins/analysis , WT1 Proteins/physiologyABSTRACT
The mitochondrion and the apicoplast of the malaria parasite, Plasmodium spp. is microscopically observed in a close proximity to each other. In this study, we tested the suitability of two different separation techniques--Percoll density gradient centrifugation and fluorescence-activated organelle sorting--for improving the purity of mitochondria isolated from the crude organelle preparation of Plasmodium falciparum. To our surprise, the apicoplast was inseparable from the plasmodial mitochondrion by each method. This implies these two plasmodial organelles are bound each other. This is the first experimental evidence of a physical binding between the two organelles in Plasmodium.
