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Associated Chromosome Trap for Identifying Long-range DNA Interactions
Published on: April 23, 2011
Molecular cloning, characterization, and chromosomal localization of a human lymphoid tyrosine kinase related to
K B Islam1, H Rabbani, C Larsson
1Center for BioTechnology, Karolinska Institute, NOVUM, Huddinge, Sweden.
Abstract:
Triggering of Ag receptors on lymphocytes induces rapid phosphorylation of several receptor-associated protein tyrosine kinases (PTKs), implicating their role in controlling cellular growth and differentiation. In this study, we report the cloning of a human cDNA encoding a nonreceptor PTK with a calculated M(r) of about 58 kDa. The kinase has an overall amino acid identity of approximately 87% with the murine Blk. However, in the unique domain there is only 58% homology and an insertion of six amino acids in the N-terminal region. The nature of this insertion suggests a functional role in membrane attachment. Northern blot analysis showed expression in all stages of B cell development and in T cell lines. The message was not observed in the nonlymphoid tissues examined. In contrast, expression of murine blk in plasma cells and T lymphocytes has not been reported. Importantly, transcripts were seen in human embryonic liver as early as 7.5 wk of gestation before the rearrangement of Ig H chain locus. Furthermore, transcripts were detected in human thymocytes and not in mature T cells. Southern blot analysis revealed polymorphism of this gene in a Caucasian population but not in a Gambian population, indicating a recent origin of this polymorphism. The gene was localized to chromosome 8p22-23. The homology at the protein level suggests that this kinase may be the human homologue of murine Blk. Expression of BLK in immature T cells suggests that BLK may play an important role in thymopoiesis.
Insights
This study identifies a novel human nonreceptor protein tyrosine kinase (PTK), BLK, crucial for lymphocyte development. Its expression in early B and T cells suggests a key role in immune cell growth and differentiation.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Protein tyrosine kinases (PTKs) are vital for lymphocyte activation, controlling cellular growth and differentiation.
- The murine Blk kinase is involved in lymphocyte signaling, but its human homologue and specific roles remain unclear.
Purpose of the Study:
- To clone and characterize a human nonreceptor PTK.
- To investigate the expression patterns and chromosomal localization of the human PTK.
- To explore the potential role of this kinase in lymphocyte development.
Main Methods:
- Cloning of human cDNA encoding a nonreceptor PTK.
- Northern blot analysis for gene expression profiling.
- Southern blot analysis for gene polymorphism.
- Chromosomal localization using genetic mapping.
Main Results:
- A human nonreceptor PTK (58 kDa) homologous to murine Blk was identified.
- Expression was detected in all B cell development stages, T cell lines, and early embryonic liver, but not in nonlymphoid tissues.
- Transcripts were found in human thymocytes but not mature T cells.
- Gene localization to chromosome 8p22-23 and population-specific polymorphism were determined.
Conclusions:
- The identified PTK is likely the human homologue of murine Blk.
- BLK expression in immature T cells suggests a significant role in thymopoiesis.
- The findings provide insights into the molecular mechanisms of immune cell development.
