The Laminin alpha Chains: Expression, Developmental Transitions, and Chromosomal Locations of alpha 1-5, Identification of Heterotrimeric Laminins 8-11, and Cloning of a Novel alpha 3 Isoform (original) (raw)

1997, The Journal of Cell Biology

Laminin trimers composed of ␣ , ␤ , and ␥ chains are major components of basal laminae (BLs) throughout the body. To date, three ␣ chains ( ␣ 1-3) have been shown to assemble into at least seven heterotrimers (called laminins 1-7). Genes encoding two additional ␣ chains ( ␣ 4 and ␣ 5) have been cloned, but little is known about their expression, and their protein products have not been identified. Here we generated antisera to recombinant ␣ 4 and ␣ 5 and used them to identify authentic proteins in tissue extracts. Immunoprecipitation and immunoblotting showed that ␣ 4 and ␣ 5 assemble into four novel laminin heterotrimers (laminins 8-11: ␣ 4 ␤ 1 ␥ 1, ␣ 4 ␤ 2 ␥ 1, ␣ 5 ␤ 1 ␥ 1, and ␣ 5 ␤ 2 ␥ 1, respectively). Using a panel of nucleotide and antibody probes, we surveyed the expression of ␣ 1-5 in murine tissues. All five chains were expressed in both embryos and adults, but each was distributed in a distinct pattern at both RNA and protein levels. Overall, ␣ 4 and ␣ 5 exhibited the broadest patterns of expression, while ex-pression of ␣ 1 was the most restricted. Immunohistochemical analysis of kidney, lung, and heart showed that the ␣ chains were confined to extracellular matrix and, with few exceptions, to BLs. All developing and adult BLs examined contained at least one ␣ chain, all ␣ chains were present in multiple BLs, and some BLs contained two or three ␣ chains. Detailed analysis of developing kidney revealed that some individual BLs, including those of the tubule and glomerulus, changed in laminin chain composition as they matured, expressing up to three different ␣ chains and two different ␤ chains in an elaborate and dynamic progression. Interspecific backcross mapping of the five ␣ chain genes revealed that they are distributed on four mouse chromosomes. Finally, we identified a novel full-length ␣ 3 isoform encoded by the Lama3 gene, which was previously believed to encode only truncated chains. Together, these results reveal remarkable diversity in BL composition and complexity in BL development.