DIFFERENTIAL SPLICING AND ALTERNATIVE POLYADENYLATION GENERATE MULTIPLE MIMECAN MESSENGER-RNA TRANSCRIPTS

We previously showed the 25-kDa corneal keratan sulfate proteoglycan t o be a translation product of the gene producing osteoglycin and propo sed the name mimecan for this gene and its product, We also demonstrat ed three mimecan RNA transcripts using Northern blot analysis, In this report, we investigate the mechanisms accounting for these transcript s, Ribonuclease protection analysis and reverse transcription-polymera se chain reaction of bovine corneal mRNA detected a mimecan transcript that lacked 278 base pairs of the 5'-untranslated region between resi dues 62 and 340. This splice variant represents the predominant form o f mimecan mRNA in bovine cornea and sclera, It was also detectable in other bovine tissues as a minor transcript. Two additional cDNA clones that were isolated contained 398 bases of nucleotide sequence at the 3'-end of mimecan cDNA, not present in the published sequence. Ribonuc lease protection analyses with the 3'-probe, which included the new se quence, allow detection of three RNA transcripts while 5'-probes recog nized only two, These results indicate that the three canonical polyad enylation sites in the 3'-untranslated region of mimican mRNA are alte rnatively selected. Possible roles for this previously undetected degr ee of diversity of mimecan RNA isoforms transcribed in the same tissue are discussed.