Desmin-positive pericytes in the chick embryo chorioallantoic membrane in response to fibroblast growth factor-2 Beatrice Nico, a Maria Grazia Ennas, b Enrico Crivellato, c Annalisa Frontino, a Domenica Mangieri, a Michela De Giorgis, a Luisa Roncali, a and Domenico Ribatti a, * a Department of Human Anatomy and Histology, University of Bari Medical School, I-70124 Bari, Italy b Department of Cytomorphology, University of Cagliari Medical School, Cagliari, Italy c Department of Medical and Morphological Researches, Section of Anatomy, University of Udine Medical School, Udine, Italy Received 22 September 2003 Available online 30 April 2004 Abstract Pericytes stabilize vessel wall, participate in the regulation of blood flow microcirculation and influence endothelial proliferation, survival, migration and maturation. Pericytes are commonly identified by molecular markers, such as desmin. The aim of this study was to analyze the pattern of distribution of desmin in the chick embryo chorioallantoic membrane (CAM) vasculature in normal condition and in response to an angiogenic cytokine, such as fibroblast growth factor-2 (FGF-2) by using conventional immunohistochemistry and confocal laser scanning microscopy. Results indicate that, in normal condition, the desmin-positive pericytes are located around the endothelial cells of the capillary plexus and of larger vessels in the intermediate mesenchyme. In response to FGF-2 numerous desmin-positive and a smooth muscle actin-negative cells are located in the mesenchyme and numerous blood vessels positive to factor VIII and desmin are recognizable near to the gelatin sponge soaked with FGF-2. These data suggest that pericytes in normal condition intervene to stabilize the wall of newly formed blood vessel, while in response to FGF-2, they detach from the wall of parental vessels and migrate, as extramural fibroblast-like desmin-positive cells, in the surrounding mesenchyme, where they modulate the angiogenic response. D 2004 Elsevier Inc. All rights reserved. Keywords: Angiogenesis; Chorioallantoic membrane; Desmin; Fibroblast growth factor-2; Pericyte Introduction Capillary wall consists of two cell types, that is, endothelial cells and pericytes indispensable for the for- mation of mature blood vessels (Doherty and Canfield, 1999). Pericytes are advential cells located within the basement membrane of capillaries and postcapillaries ven- ules. Because of their multiple cytoplasmic processes, distinctive cytoskeletal elements and envelopment of en- dothelial cells, pericytes are generally considered to be contractile cells that stabilize vessel walls and participate in the regulation of blood flow microcirculation (Shepro and Morel, 1993). Pericytes may also influence endothelial proliferation, survival, migration and maturation (Hirschi and D’Amore, 1996). The balance between the number of endothelial cells and pericytes seems to be highly con- trolled. Potential regulators include soluble factors acting in an autocrine and/or paracrine manner, mechanical forces secondary to blood flow and blood pressure, as well as homotypic and heterotypic cell contact. Pericytes are commonly identified by molecular markers, such as a smooth muscle actin, nonmuscle myosin, tropo- myosin, desmin, nestin, platelet-derived growth factor receptor-h (PDGFR-h), aminopeptidase A, aminopeptidase N (CD 13), sulfatide or high-molecular-weight melanoma- associated antigen (NG-2) (Morikawa et al., 2002). Peri- cytes on normal capillaries typically express desmin, but not a smooth muscle actin, whereas smooth muscle cells on arterioles and pericytes on venules were immunoreac- tive for both (Morikawa et al., 2002; Nehls and Drenck- hahn, 1993). Other reports have suggested that a smooth muscle actin may be considered a general marker for pericytes (Hellstrom et al., 1999; Ohlsson et al., 1999). 0026-2862/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.mvr.2004.03.005 * Corresponding author. Department of Human Anatomy and Histol- ogy, University of Bari Medical School, Piazza Giulio Cesare, 11, Policlinico, I-70124 Bari, Italy. Fax: +39-080-5478310. E-mail address: ribatti@anatomia.uniba.it (D. Ribatti). www.elsevier.com/locate/ymvre Microvascular Research 68 (2004) 13 – 19