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© The Rockefeller University Press, 0021-9525/1997//685 $5.00
The Journal of Cell Biology, Volume 137, Number 3, , 1997 685-701

Article

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



Jeffrey H. Miner*,{ddagger}, Bruce L. Patton*, Stephen I. Lentz§, Debra J. Gilbert||, William D. Snider§, Nancy A. Jenkins||, Neal G. Copeland||, and Joshua R. Sanes*

* Department of Anatomy and Neurobiology, {ddagger} Department of Internal Medicine (Renal Division), § Department of Neurology, Washington University School of Medicine, St. Louis, Missouri, 63110; and || Mammalian Genetics Laboratory, ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21702

Laminin trimers composed of {alpha}, β, and {gamma} chains are major components of basal laminae (BLs) throughout the body. To date, three {alpha} chains ({alpha}1–3) have been shown to assemble into at least seven heterotrimers (called laminins 1–7). Genes encoding two additional {alpha} chains ({alpha}4 and {alpha}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 {alpha}4 and {alpha}5 and used them to identify authentic proteins in tissue extracts. Immunoprecipitation and immunoblotting showed that {alpha}4 and {alpha}5 assemble into four novel laminin heterotrimers (laminins 8–11: {alpha}4β1{gamma}1, {alpha}4β2{gamma}1, {alpha}5β1{gamma}1, and {alpha}5β2{gamma}1, respectively). Using a panel of nucleotide and antibody probes, we surveyed the expression of {alpha}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, {alpha}4 and {alpha}5 exhibited the broadest patterns of expression, while expression of {alpha}1 was the most restricted. Immunohistochemical analysis of kidney, lung, and heart showed that the {alpha} chains were confined to extracellular matrix and, with few exceptions, to BLs. All developing and adult BLs examined contained at least one {alpha} chain, all {alpha} chains were present in multiple BLs, and some BLs contained two or three {alpha} 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 {alpha} chains and two different β chains in an elaborate and dynamic progression. Interspecific backcross mapping of the five {alpha} chain genes revealed that they are distributed on four mouse chromosomes. Finally, we identified a novel full-length {alpha}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.

Abbreviations used in this paper: BL, basal lamina; cM, centiMorgan; E, embryonic day; EHS, Englebreth-Holm-Swarm; RFLP, restriction fragment length polymorphism; RT-PCR, reverse transcription coupled–PCR.

Please address all correspondence to Joshua R. Sanes, Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110. Tel.: (314) 362-2507. Fax: (314) 747-1150.

J.H. Miner and B.L. Patton contributed equally to this work.


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