Expression patterns of murine lysosome-associated membrane protein 2 (Lamp-2) transcripts during morphogenesis

We report the isolation and characterization of the murine homologues to hu man and chicken lysosome-associated membrane protein (Lamp)-2 transcripts a nd their prevalent expression patterns during development. Lamp-2 transcrip ts code for proteins predominant in and specific for the lysosomal membrane . The function of these proteins is still under investigation. Other than i n the lysosomal membrane, Lamp-2 proteins have been detected at the plasma membrane of cells in a differentiation dependent and activation dependent m anner. They were also observed at the plasma membrane of cells, which secre te lysosomal hydrolases. Involvement of Lamp-2 in cell adhesion during such events has been proposed. A study of the developmental expression patterns of m-Lamp-2 transcripts was undertaken to help elucidate possible function s of their respective proteins. The m-Lamp-2b transcript was prevalent in n eural crest derived ganglia. The m-Lamp-2a and -2c transcripts were similar ly expressed in structures containing neural crest derived tissue with the strongest signals detected in thymus. However, m-Lamp-2a and -2c transcript expression differed in mesoderm or endoderm derived mesenchymal and epithe lial tissues. M-Lamp-2c expression was pronounced in mesenchyme early in de velopment, in limb connective tissue, and in lung parenchyma, whereas m-Lam p-2a was prevalent in the liver, the pancreas, and in differentiating kidne y epithelium, and became increasingly prominent in the epithelial lining of the digestive and the respiratory tract during development. These results correlated with the detection of m-Lamp-2 protein in these tissues. In conc lusion, all m-Lamp-2 transcripts were detected in tissues undergoing apopto sis during development requiring phagolysosome involvement. In addition, m- Lamp-2a and m-Lamp-2c transcripts were observed in epithelium and mesenchym e during the time of epithelial-mesenchymal interaction, mesenchymal-epithe lial transformation, and branching. Their expression pattern became more ti ssue and cell type specific as differentiation progressed. These patterns i ndicate a possible involvement of m-Lamp-2 proteins in cell/cell or cell/ex tracellular matrix interaction, and appear to reflect tissue and cell type specific roles of lysosomes during morphogenesis.