The human and mouse orthologous LIM-only proteins respectively encoded in chromosome 6 and 17 show a different expression pattern

Thymocytes interact with various subpopulations of thymic epithelial cells (TECs) at different stages of their development. To identify new molecules specifically expressed in TECs and/or thymic nurse cells (TNCs), we used representational difference analysis. We identified a LIM protein located on mouse chromosome 17 (m17TLP) and belonging to the family of the LIM-only proteins (LIMo). We found a new splice variant in addition to the two described A and B isoforms. The three alternative species of m17TLP are found strictly in the thymic stroma. This protein is expressed on a subpopulation of TECs and TNCs. Strikingly, we found that the human ortholog of m17TLP, located on chromosome 6 (h6LIMo), is expressed in most tissues, but not in skeletal muscle. We have identified four human splice variants of h6LIMo which differ in their carboxy-terminal regions. The sequence comprising the genomic structure suggests that CRP2 is the closest known relative of m17TLP. Although the human and mouse nucleotide sequences are 88-97% homologous, this homology is reduced to 47% in the promoter regions, which strongly suggests that their differential expression is related to their promoter regulatory activity.