title: Identification and characterization of thymus LIM protein: targeted disruption reduces thymus cellularity.
abstract: We have identified a novel LIM gene encoding the thymus LIM protein (TLP), expressed specifically in the thymus in a subset of cortical epithelial cells. TLP was identified as a gene product which is upregulated in a thymus in which selection of T cells is occurring (Rag(-/-) OT-1) compared to its expression in a thymus in which selection is blocked at the CD4+ CD8+ stage of T-cell development (Rag(-/-) Tap(-/-) OT-1). TLP has an apparent molecular mass of 23 kDa and exists as two isomers (TLP-A and TLP-B), which are generated by alternative splicing of the message. The sequences of TLP-A and TLP-B are identical except for the C-terminal 19 or 20 amino acids. Based on protein sequence alignment, TLP is most closely related to the cysteine-rich proteins, a subclass of the family of LIM-only proteins. In both medullary and cortical thymic epithelial cell lines transduced with TLP, the protein localizes to the cytoplasm but does not appear to be strongly associated with actin. In immunohistochemical studies, TLP seems to be localized in a subset of epithelial cells in the cortex and is most abundant near the corticomedullary junction. We generated mice with a targeted disruption of the Tlp locus. In the absence of TLP, thymocyte development and thymus architecture appear to be normal but thymocyte cellularity is reduced by approximately 30%, with a proportional reduction in each subpopulation.
authors.affiliation: Howard Hughes Medical Institute and Department of Immunology, University of Washington, Seattle, WA 98195, USA.
authors.forename: J
authors.initials: J
authors.lastname: Kirchner
authors.forename: K A
authors.initials: KA
authors.lastname: Forbush
authors.forename: M J
authors.initials: MJ
authors.lastname: Bevan
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D015704:CD4 Antigens / Q000096:biosynthesis; D016827:CD8 Antigens / Q000096:biosynthesis; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005434:Flow Cytometry; D005982:Glutathione Transferase / Q000378:metabolism; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000737:chemistry*; D015151:Immunoblotting; D007150:Immunohistochemistry; D060588:LIM Domain Proteins; D054461:Lim Kinases; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D008957:Models, Genetic; D008969:Molecular Sequence Data; D011494:Protein Kinases / Q000096:biosynthesis* / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012190:Retroviridae / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D000199:Actins; D015704:CD4 Antigens; D016827:CD8 Antigens; C441450:Crip3 protein, mouse; D018076:DNA, Complementary; D018398:Homeodomain Proteins; D060588:LIM Domain Proteins; D011993:Recombinant Fusion Proteins; D012313:RNA; D004247:DNA; D005982:Glutathione Transferase; D011494:Protein Kinases; D054461:Lim Kinases; C515893:Limk1 protein, mouse