HUMAN LAMININ-M CHAIN (MEROSIN) - COMPLETE PRIMARY STRUCTURE, CHROMOSOMAL ASSIGNMENT, AND EXPRESSION OF THE M-CHAIN AND A-CHAIN IN HUMAN FETAL TISSUES

The primary structure of the human laminin M chain was determined from cDNA clones isolated from human placental libraries. The clones cover ed a total of 6,942 bp, with 49-bp encoding a 5' end untranslated regi on and 6,893-bp coding for a translated sequence. The complete human l aminin M chain contains a 22-residue signal peptide and 3,088 residues of the mature M chain. The M chain has a domain structure similar to that of the human and mouse A chains. The homology between the two hum an laminin heavy chains is highest in the short arm region and lowest in the long arm helical domain I + II. Northern blot analysis of human fetal tissues showed that the M chain was expressed in most tissues s uch as cardiac muscle, pancreas, lung, spleen, kidney, adrenal gland, skin, testis, meninges, choroid plexus, and some other regions of the brain, but not in liver, thymus, and bone. In situ hybridization local ized the expression of the M chain gene to cells of mesenchymal origin . In contrast, expression of the A chain was observed only in kidney, testis, neuroretina and some region of brain as determined by Northern analyses. Epithelial and endothelial cells were negative for both M a nd A chain gene transcripts. The gene for the human M chain (LAMM) was localized to chromosome 6q22-->23.