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CD9, a major platelet cell surface glycoprotein, is a ROCA antigen and is expressed in the nervous system
Z Kaprielian1, K O Cho, M Hadjiargyrou
1Biology Division, California Institute of Technology, Pasadena 91125.
Insights
Researchers identified rat CD9, a cell surface protein, in neural tissues using monoclonal antibodies. CD9 is expressed by peripheral neurons and Schwann cells, suggesting a role in nervous system intercellular signaling.
Area of Science:
- Neuroscience
- Cell Biology
- Immunology
Background:
- Monoclonal antibodies (mAbs) ROCA1, ROCA2, and B2C11 recognize a 26 kDa cell surface protein.
- This protein shares homology with human CD9, a tetraspan protein involved in hematopoietic cell signaling.
Purpose of the Study:
- To identify the 26 kDa cell surface protein recognized by ROCA mAbs.
- To investigate the expression and potential role of rat CD9 in the nervous system.
Main Methods:
- Amino acid sequencing of the purified 26 kDa protein.
- Polymerase Chain Reaction (PCR) to obtain rat CD9 cDNA.
- Immunoprecipitation using mAbs and transfected cells.
- mRNA expression analysis via in situ hybridization and immunoblotting.
Main Results:
- The ROCA cell surface antigen was confirmed to be rat CD9.
- Rat CD9 mRNA is widely expressed in neural tissues, including peripheral neurons, Schwann cells, and adrenal chromaffin cells.
- CD9 mRNA levels in developing sciatic nerve correlate with myelin gene expression.
- Unlike the ROCA1 epitope, rat CD9 protein is not expressed in a rostrocaudal gradient.
Conclusions:
- Rat CD9 is expressed in various neural cell types.
- CD9 may play a role in intercellular signaling within the nervous system.
- CD9 represents a cell surface protein found in both hematopoietic and neural cells.
Abstract:
We previously generated a monoclonal antibody (mAb), ROCA1, which binds preferentially to rostral versus caudal sympathetic ganglia and intercostal nerves. Two other mAbs, ROCA2 and B2C11, bind to the same structures but not in rostrocaudal gradients. All three mAbs recognize a 26 kDa cell surface protein. Amino acid sequence data obtained from the affinity purified 26 kDa protein showed some homology with human CD9, a tetraspan protein implicated in intercellular signaling in hematopoietic cells. Using the PCR, we obtained cDNA clones representing the entire rat CD9 coding sequence from sciatic nerve and sympathetic ganglia. ROCA1, ROCA2, and B2C11 each immunoprecipitate a 26 kDa protein from CHO cells stably transfected with one of the clones, demonstrating that the ROCA cell surface antigen is indeed rat CD9. We find that CD9 mRNA is widely expressed, with particularly high levels present in a number of neural tissues. In situ hybridization demonstrates that peripheral neurons and Schwann cells, as well as adrenal chromaffin cells express CD9 mRNA. Consistent with immunoblot analyses showing that, unlike the ROCA1 epitope, the 26 kDa protein is not expressed in a rostrocaudal gradient, we find similar levels of rat CD9 mRNA in rostral and caudal intercostal nerves. In developing postnatal rat sciatic nerve, CD9 mRNA levels are coordinately regulated with the expression of myelin genes. These results provide another example of a cell surface protein expressed by both hematopoietic and neural cells, and suggest a role for CD9 in intercellular signaling in the nervous system.