The distribution of subunits of the basement membrane proteins laminin and merosin in human and rabbit tissue was studied by immunofluorescence using monoclonal antibodies. The laminin A chain is present in epithelial, endothelial, and smooth muscle basement membranes. Merosin, as defined by its heavy chain M, is present in striated muscle and peripheral nerve. The A subunit colocalizes with at least two B subunits: B2 plus either B1 or the recently discovered B1 homologue S. The M subunit most often colocalizes with B1 and B2. Exceptions include the myotendinous junction, where M colocalizes with S, and the trophoblast basement membrane, where the M subunit colocalizes with S as well as B1. The presence of all five known subunits of the laminin family in placenta allowed isolation of their parent molecules in native form by the use of monoclonal antibodies in affinity chromatography. Four different heterotrimeric proteins could be identified: B1 chain-containing laminin (A-B1-B2), S chain-containing laminin (A-S-B2), B1-containing merosin (M-B1-B2), and S-containing merosin (M-S-B2). The data show that the proteins in the laminin family are heterotrimers composed of one heavy and two light chains; that most basement membranes contain predominantly one protein of the laminin family; and that laminin, as defined by the A subunit, has a much more restricted distribution than previously thought.
A complementary DNA clone corresponding to a 4.2-kilobase transcript that is present in the Xenopus oocyte and newly transcribed in the neurula stages of development has been isolated. This messenger RNA encodes a 155-amino acid protein that is 84% identical to the human basic fibroblast growth factor (bFGF). When expressed in Escherichia coli and purified, the Xenopus FGF induced mesoderm in animal cell blastomeres as measured by muscle actin expression. Immunoblots with an antibody to a Xenopus FGF peptide show that the oocyte and early embryo contain a store of the FGF polypeptide at high enough concentrations to induce mesoderm. The presence of FGF in the oocyte, together with the apparent lack of a secretory signal sequence in the protein, suggest that the regulation of mesoderm induction may involve novel mechanisms that occur after the translation of FGF.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.