137 Ann. N.Y. Acad. Sci. 1040: 137–139 (2005). © 2005 New York Academy of Sciences. doi: 10.1196/annals.1327.017 Analysis of Rab18 and a New Golgin in the Secretory Pathway M. M. MALAGÓN, a D. CRUZ, a R. VÁZQUEZ-MARTÍNEZ, a J. R. PEINADO, a Y. ANOUAR, b M. C. TONON, b H. VAUDRY, b F. GRACIA-NAVARRO, a AND J. P. CASTAÑO a a Department of Cell Biology, Physiology, and Immunology, University of Córdoba, 14014 Córdoba, Spain b Laboratory of Cellular and Molecular Neuroendocrinology, University of Rouen, 76821 Mont-Saint-Aignan, France ABSTRACT: Two new amphibian genes have been isolated and characterized from frog melanotropes, and the level of expression of these genes is related to the secretory status of the cells. Both genes, Rab18 and a novel member of the golgin family of proteins, are ubiquitously expressed in endocrine and non- endocrine tissues, and their corresponding proteins appear to show intracellular distributions associated with discrete vesicular and tubular structures, respec- tively, suggesting that they may play relevant roles in the regulation of the secretory pathway. KEYWORDS: secretory pathway; Rab proteins; golgin proteins INTRODUCTION We have previously shown that the frog intermediate lobe consists of two melano- trope subtypes, which are separable by gradient centrifugation. By virtue of having opposite secretory phenotypes, they were named secretory and storage melano- tropes. Secretory cells are poorly granulated, but display high biosynthetic and secretory rates, whereas storage cells exhibit high content of secretory granules and low biosynthetic and secretory rates. 1 A differential display of genes expressed in these subpopulations enabled us to isolate and characterize two novel amphibian genes, which are overexpressed in and likely related to the storage phenotype: Rab18 and a golgin-like gene. RESULTS AND DISCUSSION Rab18 belongs to a large family of small GTPase proteins that participate in recognition processes between vesicles and their target membranes, and therefore Address for correspondence: M. M. Malagón, Department of Cell Biology, Physiology, and Immunology, University of Córdoba, 14014 Córdoba, Spain. Voice: +34-957-218594; fax: +34- 957-218634. bc1mapom@uco.es