Alternatively Spliced, Germline Jα11-2-Cα mRNAs Are the Predominant T Cell Receptor α Transcripts in Mouse Kidney
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We recently reported the expression of a truncated T cell receptor (TCR) α mRNA in kidney and brain of normal mice. In the kidney, the truncated TCR α transcript was expressed by bone marrow-dependent, non-T large interstitial cells located predominantly in the medulla. Here, we report the molecular characterization of the truncated TCR α transcript from kidney. Using a modified anchored-PCR (A-PCR) technique and directional cloning, 37 cDNA clones extending 5' of the Cα region were generated. cDNA sequencing showed that 29 of the clones (78%) originated in the Jα 11-2 region. Of these clones, 17 started upstream or in the Jα 11-2 exon and contained the entire Jα 11-2 sequence correctly spliced to the first Cα exon. Analysis of the sequence revealed the presence of multiple stop codons in all three reading frames. The other 12 clones originated further upstream of the Jα 11-2 exon and did not include the Jα 11-2 exon, but rather arose from the joining of a cryptic splice donor signal to the usual TCR α C splice acceptor. This alternatively spliced transcript contained an open reading frame extending from the upstream Jα 11-2 region to 82 nucleotides downstream of the beginning of the TCR C α region, and potentially encoded a 36 amino acid polypeptide. The remaining eight clones all contained the Jα TA61 region correctly spliced to Cα with two of these extending upstream of the Jα TA61 exon. The predominance of Jα 11-2-Cα containing clones was confirmed by RNase protection assay using total RNA from kidney and spleen of scid mice. The 3' region of the transcript contained a fully conserved, correctly spliced TCR α C region which was polyadenylated at the 3' end. The truncated TCR a mRNA could be detected in preparations of cytoplasmic RNA, indicating that this transcript follows a normal RNA processing pathway. Our results demonstrate that the truncated TCR α mRNA expressed in normal mouse kidney is a germline J-C transcript resulting from transcription initiated predominantly upstream of the Jα 11-2 region. This germline transcript in the kidney is undergoing alternative splicing leading to the appearance of an open reading frame coding for a short polypeptide. These results suggest that the product of this transcript may be functionally relevant.