Cloning and Characterization of Two Forms of Bovine Polymeric Immunoglobulin Receptor cDNA

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Abstract
The polymeric immunoglobulin receptor (transmembrane secretory component) mediates transcellular transport of dimeric immunoglobulin A (IgA) and pentameric IgM in glandular and mucosal epithelial cells. cDNAs encoding two forms of the bovine polymeric immunoglobulin receptor (plgR) have been cloned and sequenced. The long form contains 3,527 bp and predicts a single open reading frame of 2,271 bp encoding a protein of 757 bp. The extracellular part contains five immunoglobulin (Ig)-like domains. The shorter form lacks the region from residues 458–1,111 corresponding to Ig-like domains 2 and 3. In Northern blot analysis of various bovine tissues, only the long form of pIgR mRNA was detected. By using the reverse transcription–polymerase chain reaction (RT-PCR), both forms were detected. An alignment of the cytoplasmic tail of the pIgR from bovine, human, rabbit, and rat revealed highly conserved areas that may reflect the importance of these regions for intracellular sorting of the receptor.