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Nucleocytoplasmic Shuttling of lgl2 Is Developmentally Regulated in Fetal Lung

McGill University-Montreal Children's Hospital Research Institute, Department of Anatomy and Cell Biology, Department of Human Genetics, and Department of Pediatrics, McGill University, Montreal, Quebec, Canada; Lung Biology Research, Research Institute, Hospital for Sick Children, Toronto; and Departments of Pediatrics and Physiology, University of Toronto, Toronto, Ontario, Canada

Address correspondence to: Feige Kaplan, McGill University-Montreal Children's Hospital Research Institute, 4060 St Catherine St West, Rm 236, Montreal, PQ, H3Z 2Z3 Canada. E-mail: feige.kaplan{at}mcgill.ca

To investigate molecular mechanisms of lung organogenesis, we searched for glucocorticoid-inducible genes in developing lung. We cloned LGL2, a developmentally and hormonally regulated gene in fetal lung (Zhang, C., N. B. Sweezey, S. Gagnon, B. Muskat, D. Koehler, M. Post, and F. Kaplan. 2000. A novel karyopherin-ß homolog is developmentally and hormonally regulated in fetal lung. Am. J. Respir. Cell Mol. Biol. 22:451–459). A comparison of lgl2 protein to sequences in the genome database suggested that lgl2 is a nuclear transport receptor. We report on the functional characterization of lgl2 as an importin ß protein and on the developmental regulation of its nucleocytoplasmic shuttling in fetal lung. We investigated the subcellular localization and Ran-binding properties of lgl2 and its N- and C-terminal regions. We used fluorescence recovery after photobleaching and fluorescence loss in photobleaching to study nucleocytoplasmic shuttling of lgl2. We showed that N-terminal lgl2 supports shuttling at a reduced rate. We showed that the nucleocytoplasmic distribution of lgl2 favors the nucleus in fetal lung and that lgl2 enters the nucleus much more rapidly at fetal Day 18 than at Day 21. Total nuclear recovery of lgl2 was dramatically different at the two time points. Early in development, nuclear import of transcription factors in response to hormones and growth agonists regulates prominent signal transduction pathways that govern lung organogenesis. We speculate that lgl2 may be one important modulator of this process.

Abbreviations: enhanced yellow fluorescence protein, EYFP • fluorescence loss in photobleaching, FLIP • fluorescence recovery after photobleaching, FRAP • nuclear pore complex, NPC • polymerase chain reaction, PCR