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Chains: Expression, Developmental Transitions,
and Chromosomal Locations of
1-5, Identification of
Heterotrimeric Laminins 8-11, and Cloning of a Novel
3 Isoform




* Department of Anatomy and Neurobiology, Laminin trimers composed of
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
,
, 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 expression 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.
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