Differential expression of mouse laminin gamma2 and gamma2* chain transcripts

Laminins are large heterotrimeric basement membrane proteins that consist of alpha, beta, and gamma chains. We have previously shown that the human gamma2 and gamma2* transcripts result from the alternative use of the LAMC2 gene 3'-end exons. To explore the biological significance of the alternative gamma2 transcripts, we isolated the cDNA coding for the mouse laminin gamma2* transcript, characterized the 3'-end of the murine LAMC2 gene, and studied the expression of alternative gamma2 transcripts in several mouse tissues. The sequence reported here is the first one containing a full-length gamma2* 3'-UTR from any species. The mouse gamma2* transcript is 4110 bases and encodes a putative polypeptide of 1110 amino acids. This polypeptide lacks the C-terminal cysteine residue thought to be important for heterotrimer formation. The mouse gamma2* transcript was found to be expressed in several tissues by polymerase chain reaction (PCR), but at very low levels. The clearest signals were obtained on embryonic day 7, and in heart and testis of adult tissues. When the laminin gamma2* transcript expression pattern was compared with that of the gamma2 chain, a similar tissue distribution was observed. There was, however, a significant difference in expression levels. The longer gamma2 transcript was found to be much more abundant than the shorter gamma2* variant. Moreover, by whole-mount in situ hybridization, the shorter gamma2* form was localized in the mesenchyme of the developing kidney whereas the longer gamma2 form was exclusively present in the epithelium of the Wolffian (nephric) duct and ureteric bud. The results indicate different functions for the gamma2 variants.