Glomulin is predominantly expressed in vascular smooth muscle cells in the embryonic and adult mouse Brendan A.S. McIntyre, Pascal Brouillard, Virginie Aerts, Ilse Gutierrez-Roelens, Miikka Vikkula * Laboratory of Human Molecular Genetics, Christian de Duve Institute of Cellular Pathology and Universite ´ catholique de Louvain, Avenue Hippocrate 74 (þ 5), BP 75.39, 1200 Brussels, Belgium Received 13 June 2003; received in revised form 28 August 2003; accepted 23 September 2003 Abstract Mutations in the glomulin gene result in dominantly inherited vascular lesions of the skin known as glomuvenous malformations (GVMs). These lesions are histologically distinguished by their distended vein-like channels containing characteristic ‘glomus cells’, which appear to be incompletely or improperly differentiated vascular smooth muscle cells (VSMCs). The function of glomulin is currently unknown. We studied glomulin expression during murine development (E9.5 days post-coitum until adulthood) by non-radioactive in situ hybridization. Glomulin was first detected at E10.5 dpc in cardiac outflow tracts. Later, it showed strong expression in VSMCs as well as a limited expression in the perichondrium. At E11.5-14.5 dpc glomulin RNA was most abundant in the walls of the large vessels. At E16.5 dpc expression was also detectable in smaller arteries and veins. The high expression of glomulin in murine vasculature suggests an important role for glomulin in blood vessel development and/or maintenance, which is supported by the vascular phenotype seen in GVM patients with mutations in this gene. q 2003 Elsevier B.V. All rights reserved. Keywords: Glomulin; Glomuvenous malformation; Vascular smooth muscle cell; Glomus cell; FAP68; Vasculogenesis; Angiogenesis; Perichondrium; Glomangioma; Glomus tumor 1. Results and discussion The glomulin gene was found by positional cloning (Boon et al., 1999; Brouillard et al., 2000, 2002), to be mutated in autosomal dominantly inherited glomuvenous malformations (GVMs), also known as ‘glomangiomas’, a clinical and radiological subtype of venous malformations (Brouillard and Vikkula, 2003; Vikkula et al., 2001). Most mutations found are presumed to result in truncations of the protein, most likely causing loss-of-function (Brouillard et al., 2002). However, as not all cutaneous veins are affected, the development of lesions is likely to need an additional event. We believe that this results in a complete localized loss of glomulin function, as evidenced by a somatic ‘second hit’ identified in the affected tissue of one GVM patient (Brouillard et al., 2002). Upon histological examination, GVMs are formed of distended vein-like channels containing variable numbers of poorly differentiated vascular smooth muscle cells (VSMCs), termed ‘glomus cells’, in their walls. Using immunohistochemistry, glomus cells are found to stain positively for smooth muscle cell a-actin and vimentin, but negatively for desmin, von Willebrand factor and S-100 (Kato et al., 1990). In contrast, hereditary mucocutaneous venous malformations, caused by mutations in the angio- poietin receptor TIE-2, are characterized by a relative lack of normally differentiated VSMCs (Vikkula et al., 1996). Clini- cally, GVM lesions generally take on a purple-blue colored, cobblestone appearance and are painful upon palpation. Previous studies using the yeast two-hybrid assay have shown full-length glomulin (termed FAP68 by the authors) to associate with the intracellular portion of the proto- oncogene c-Met, also known as hepatocyte growth factor receptor (Grisendi et al., 2001). Another yeast two-hybrid study pulled out a protein with a sequence corresponding to the first three-quarters of the glomulin sequence, which was termed FAP48 for FK506-binding protein associated protein of 48 kDa (Chambraud et al., 1996). This truncated form of glomulin with an altered carboxy-terminal end was 1567-133X/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.modgep.2003.09.007 Gene Expression Patterns 4 (2004) 351–358 www.elsevier.com/locate/modgep * Corresponding author. Tel.: þ 32-2-764-7496; fax: þ32-2-764-7460. E-mail address: vikkula@bchm.ucl.ac.be (M. Vikkula).