Differential expression of mouse laminin γ2 and γ2* chain transcripts

Laminins are large heterotrimeric basement membrane proteins that consist of α, β, and γ chains. We have previously shown that the human γ2 and γ2* transcripts result from the alternative use of the LAMC2 gene 3'-end exons. To explore the biological significance of the alternative γ2 transcripts, we isolated the cDNA coding for the mouse laminin γ2* transcript, characterized the 3'-end of the murine LAMC2 gene, and studied the expression of alternative γ2 transcripts in several mouse tissues. The sequence reported here is the first one containing a full-length γ2* 3'-UTR from any species. The mouse γ2* 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 γ2* 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 γ2* transcript expression pattern was compared with that of the γ2 chain, a similar tissue distribution was observed. There was, however, a significant difference in expression levels. The longer γ2 transcript was found to be much more abundant than the shorter γ2* variant. Moreover, by whole-mount in situ hybridization, the shorter γ2* form was localized in the mesenchyme of the developing kidney whereas the longer γ2 form was exclusively present in the epithelium of the Wolffian (nephric) duct and ureteric bud. The results indicate different functions for the γ2 variants.