Expression of s-laminin and laminin in the developing rat central nervous system.
The extracellular matrix component, s-laminin, is a homologue of the B1 subunit of laminin. S-laminin is concentrated in the synaptic cleft at the neuromuscular junction and contains a site that is adhesive for motor neurons, suggesting that it may influence neuromuscular development. To ascertain whether s-laminin may also play roles in the genesis of the central nervous system, we have examined its expression in the brain and spinal cord of embryonic and postnatal rats. S-laminin was not detectable in synapse-rich areas of adults. However, s-laminin was present in discrete subsets of three laminin-containing structures: (1) In the developing cerebral cortex, laminin and s-laminin were expressed in the subplate, a transient layer through which neuroblasts migrate and cortical afferents grow. Both laminin and s-laminin disappeared as embryogenesis proceeded; however, laminin was more widely distributed and present longer than s-laminin. (2) In the developing spinal cord, laminin was present throughout the pia. In contrast, s-laminin was concentrated in the pia that overlies the floor plate, a region in which extracellular cues have been postulated to guide growing axons. (3) In central capillaries, s-laminin appeared perinatally, an interval during which the blood-brain barrier matures. In contrast, laminin was present in capillary walls of both embryos and adults. To extend our immunohistochemical results, we used biochemical methods to characterize s-laminin in brain. We found that authentic s-laminin mRNA is present in the embryonic brain, but that brain-derived s-laminin differs (perhaps by a posttranslational modification) from that derived from nonneural tissues. We also used tissue culture methods to show that glia are capable of synthesizing "brain-like" s-laminin, and of assembling it into an extracellular matrix. Thus, glia may be one cellular source of s-laminin in brain. Together, these results demonstrate that s-laminin is present in the developing central nervous system, and raise the possibility that this molecule may influence developmental processes.
Hunter
D D
DD
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Llinas
R
R
Ard
M
M
Merlie
J P
JP
Sanes
J R
JR
D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D002196:Capillaries / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D002490:Central Nervous System / Q000196:embryology / Q000378:metabolism*; D002540:Cerebral Cortex / Q000737:chemistry / Q000196:embryology / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D007150:Immunohistochemistry; D007797:Laminin / Q000096:biosynthesis*; D009419:Nerve Tissue Proteins / Q000737:chemistry; D009457:Neuroglia / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D011247:Pregnancy; D012343:RNA, Transfer / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley
D007797:Laminin; D009419:Nerve Tissue Proteins; C058783:laminin beta2; D012343:RNA, Transfer